diff --git a/Makefile b/Makefile
index aeae4bdc..669b43b7 100644
--- a/Makefile
+++ b/Makefile
@@ -5,7 +5,7 @@ format:
 test:
 	black . --check
 	isort . --check --diff --skip checkpoint --skip wandb --skip data
-	env PYTHONPATH=. pytest --pylint --flake8 --cov=tests --ignore=checkpoint --ignore=data --ignore=wandb --ignore tests/integration
+	env PYTHONPATH=. pytest --pylint --flake8 --cov=tests --ignore=checkpoint --ignore=data --ignore=wandb --ignore tests/integration --ignore example
 
 integration-test:
 	env PYTHONPATH=. pytest tests/integration --cov=tests
diff --git a/example/__init__.py b/example/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/example/custom_agent.py b/example/custom_agent.py
new file mode 100644
index 00000000..57831f0b
--- /dev/null
+++ b/example/custom_agent.py
@@ -0,0 +1,34 @@
+# -*- coding: utf-8 -*-
+"""Custom Agent for DQN.
+   This is example for using custom agent.
+   In this example, custom agent use state as exponential.
+   You can customize any function e.g) select_aciton, train ... etc.
+
+   To use custom agent just decorate class to build and import in main function.
+
+    - Author: Jiseong Han
+    - Contact: jisung.han@medipixel.io
+"""
+
+import numpy as np
+import torch
+
+from rl_algorithms.common.helper_functions import numpy2floattensor
+from rl_algorithms.dqn.agent import DQNAgent
+from rl_algorithms.registry import AGENTS
+
+
+@AGENTS.register_module
+class CustomDQN(DQNAgent):
+    """Example Custom Agent for DQN"""
+
+    # pylint: disable=no-self-use
+    def _preprocess_state(self, state: np.ndarray) -> torch.Tensor:
+        """Preprocess state so that actor selects an action."""
+        state = np.exp(state)
+        state = numpy2floattensor(state, self.learner.device)
+        return state
+
+    def train(self):
+        """Custom train."""
+        pass
diff --git a/example/custom_dqn.yaml b/example/custom_dqn.yaml
new file mode 100644
index 00000000..93604b56
--- /dev/null
+++ b/example/custom_dqn.yaml
@@ -0,0 +1,38 @@
+type: "CustomDQN" #Custom Agent name
+hyper_params:
+  gamma: 0.99
+  tau: 0.005
+  buffer_size: 10000  # openai baselines: 10000
+  batch_size: 64  # openai baselines: 32
+  update_starts_from: 100  # openai baselines: 10000
+  multiple_update: 1  # multiple learning updates
+  train_freq: 1  # in openai baselines, train_freq = 4
+  gradient_clip: 10.0  # dueling: 10.0
+  n_step: 3
+  w_n_step: 1.0
+  w_q_reg: 0.0000001
+  per_alpha: 0.6  # openai baselines: 0.6
+  per_beta: 0.4
+  per_eps: 0.000001
+  max_epsilon: 1.0
+  min_epsilon: 0.01  # openai baselines: 0.01
+  epsilon_decay: 0.00001  # openai baselines: 1e-7 / 1e-1
+
+learner_cfg:
+  type: "CustomDQNLearner" #Custom Learner name
+  loss_type:
+    type: "C51Loss"
+  backbone:
+  head:
+    type: "C51DuelingMLP"
+    configs: 
+      hidden_sizes: [128, 64]
+      v_min: -300
+      v_max: 300
+      atom_size: 1530
+      output_activation: "identity"
+      use_noisy_net: False
+  optim_cfg:
+    lr_dqn: 0.0001
+    weight_decay: 0.0000001
+    adam_eps: 0.00000001
diff --git a/example/custom_learner.py b/example/custom_learner.py
new file mode 100644
index 00000000..7c0682ab
--- /dev/null
+++ b/example/custom_learner.py
@@ -0,0 +1,34 @@
+"""This is example to use custom learner that inherit DQNLearner.
+    You need to decorate class to register your own Learner to build.
+    And import custom learner on main file.
+
+    If you want to make custom learner, you can inherit BaseLeaner or Learner.
+    If you make your own learner, you need to change config file to build.
+
+    - Author: Jiseong Han
+    - Contact: jisung.han@medipixel.io
+"""
+from typing import Tuple, Union
+
+import numpy as np
+import torch
+
+from rl_algorithms.common.abstract.learner import TensorTuple
+from rl_algorithms.dqn.learner import DQNLearner
+from rl_algorithms.registry import LEARNERS
+
+
+@LEARNERS.register_module
+class CustomDQNLearner(DQNLearner):
+    """Example of Custom DQN learner."""
+
+    def _init_network(self):
+        return super()._init_network()
+
+    def update_model(
+        self, experience: Union[TensorTuple, Tuple[TensorTuple]]
+    ) -> Tuple[torch.Tensor, torch.Tensor, list, np.ndarray]:  # type: ignore
+        """
+        Custom Update model with experience.
+        """
+        pass
diff --git a/example/run_custom_env.py b/example/run_custom_env.py
new file mode 100644
index 00000000..55d8d2b4
--- /dev/null
+++ b/example/run_custom_env.py
@@ -0,0 +1,179 @@
+# -*- coding: utf-8 -*-
+"""Train or test algorithms on Custom Environment.
+
+- Author: Jiseong Han
+- Contact: jisung.han@medipixel.io
+"""
+
+import argparse
+import datetime
+
+import gym
+import numpy as np
+
+from rl_algorithms import build_agent
+import rl_algorithms.common.env.utils as env_utils
+import rl_algorithms.common.helper_functions as common_utils
+from rl_algorithms.utils import YamlConfig
+
+
+def parse_args() -> argparse.Namespace:
+    # configurations
+    parser = argparse.ArgumentParser(description="Pytorch RL algorithms")
+    parser.add_argument(
+        "--seed", type=int, default=777, help="random seed for reproducibility"
+    )
+    parser.add_argument(
+        "--integration-test",
+        dest="integration_test",
+        action="store_true",
+        help="for integration test",
+    )
+    parser.add_argument(
+        "--cfg-path",
+        type=str,
+        default="rl_algorithms/example/custom_dqn.yaml",
+        help="config path",
+    )
+    parser.add_argument(
+        "--test", dest="test", action="store_true", help="test mode (no training)"
+    )
+    parser.add_argument(
+        "--load-from",
+        type=str,
+        default=None,
+        help="load the saved model and optimizer at the beginning",
+    )
+    parser.add_argument(
+        "--off-render", dest="render", action="store_false", help="turn off rendering"
+    )
+    parser.add_argument(
+        "--render-after",
+        type=int,
+        default=0,
+        help="start rendering after the input number of episode",
+    )
+    parser.add_argument(
+        "--log", dest="log", action="store_true", help="turn on logging"
+    )
+    parser.add_argument(
+        "--save-period", type=int, default=100, help="save model period"
+    )
+    parser.add_argument(
+        "--episode-num", type=int, default=1500, help="total episode num"
+    )
+    parser.add_argument(
+        "--max-episode-steps", type=int, default=300, help="max episode step"
+    )
+    parser.add_argument(
+        "--interim-test-num",
+        type=int,
+        default=10,
+        help="number of test during training",
+    )
+
+    return parser.parse_args()
+
+
+class CustomEnv(gym.Env):
+    """Custom Environment for example."""
+
+    metadata = {"render.modes": ["human"]}
+
+    def __init__(self):
+        super(CustomEnv, self).__init__()
+        self.action_space = gym.spaces.Discrete(2)
+        self.observation_space = gym.spaces.Box(low=-3, high=3, shape=(1,))
+        self.pos = 0
+
+    def step(self, action):
+        """
+        Reach Position as 3 get +1 reward.
+        else if Position is lower than  then -1 reward.
+        else get -0.1.
+        """
+        action = -1 if action == 0 else 1
+        self.pos += action
+        if self.pos <= -3:
+            reward = -1
+        elif self.pos >= 3:
+            reward = 1
+        else:
+            reward = -0.1
+        done = abs(self.pos) >= 3
+
+        return np.array([self.pos]), reward, done, {}
+
+    def reset(self):
+        self.pos = 0
+        return np.array([self.pos])
+
+    def render(self, mode="human"):
+        render_state = [[] for _ in range(7)]
+        render_state[self.pos + 3] = [0]
+        print(
+            "################################\n",
+            render_state,
+            "\n################################",
+        )
+
+
+def main(custom_env):
+    """Main."""
+    args = parse_args()
+
+    env_name = type(custom_env).__name__
+    env, max_episode_steps = env_utils.set_env(custom_env, args.max_episode_steps)
+
+    # set a random seed
+    common_utils.set_random_seed(args.seed, env)
+
+    # run
+    NOWTIMES = datetime.datetime.now()
+    curr_time = NOWTIMES.strftime("%y%m%d_%H%M%S")
+
+    cfg = YamlConfig(dict(agent=args.cfg_path)).get_config_dict()
+
+    # If running integration test, simplify experiment
+    if args.integration_test:
+        cfg = common_utils.set_cfg_for_intergration_test(cfg)
+
+    env_info = dict(
+        name=env_name,
+        observation_space=env.observation_space,
+        action_space=env.action_space,
+        is_atari=False,
+    )
+    log_cfg = dict(agent=cfg.agent.type, curr_time=curr_time, cfg_path=args.cfg_path)
+    build_args = dict(
+        env=env,
+        env_info=env_info,
+        log_cfg=log_cfg,
+        is_test=args.test,
+        load_from=args.load_from,
+        is_render=args.render,
+        render_after=args.render_after,
+        is_log=args.log,
+        save_period=args.save_period,
+        episode_num=args.episode_num,
+        max_episode_steps=max_episode_steps,
+        interim_test_num=args.interim_test_num,
+    )
+    agent = build_agent(cfg.agent, build_args)
+
+    if not args.test:
+        agent.train()
+    else:
+        agent.test()
+
+
+if __name__ == "__main__":
+    ###################################################################################
+    # To use custom agent and learner, import custom agent and learner.
+    from custom_agent import CustomDQN  # noqa: F401
+    from custom_learner import CustomDQNLearner  # noqa: F401
+
+    # Declare custom environment here.
+    env = CustomEnv()
+    ###################################################################################
+    main(env)
diff --git a/requirements.txt b/requirements.txt
index 27bec5e2..cfaf777c 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,5 +1,5 @@
 numpy==1.18.0
-torch==1.6.0
+torch>=1.6.0
 gym==0.17.3
 atari-py==0.2.6
 box2d-py==2.3.8
diff --git a/rl_algorithms/common/abstract/agent.py b/rl_algorithms/common/abstract/agent.py
index 74543dfd..8c530882 100644
--- a/rl_algorithms/common/abstract/agent.py
+++ b/rl_algorithms/common/abstract/agent.py
@@ -157,7 +157,7 @@ def _test(self, interim_test: bool = False):
                 step += 1
 
             print(
-                "[INFO] test %d\tstep: %d\ttotal score: %d" % (i_episode, step, score)
+                "[INFO] test %d\tstep: %d\ttotal score: %.2f" % (i_episode, step, score)
             )
             score_list.append(score)