diff --git a/khaosz/trainer/callback.py b/khaosz/trainer/callback.py
index e7cdf25..bb0a3ea 100644
--- a/khaosz/trainer/callback.py
+++ b/khaosz/trainer/callback.py
@@ -1,3 +1,4 @@
+import os
 from tqdm import tqdm
 from khaosz.core.parameter import Checkpoint
 from torch.nn.utils import clip_grad_norm_
@@ -104,6 +105,13 @@ class CheckpointCallback(TrainerCallback):
         self.checkpoint_interval = checkpoint_interval
         self.last_ckpt_iter = 0
     
+    @staticmethod
+    def _save_checkpoint(trainer: 'Trainer'):
+        current_iter = len(trainer.checkpoint.loss_list)
+        save_path = os.path.join(trainer.train_config.checkpoint_dir, f"iter_{current_iter}")
+        trainer.checkpoint.optim_state = trainer.train_config.optimizer.state_dict()
+        trainer.checkpoint.save(save_path)
+    
     def on_train_begin(self, trainer: 'Trainer', **kwargs):
         _ = trainer
         checkpoint = cast(Checkpoint, kwargs.get('checkpoint'))
@@ -112,14 +120,14 @@ class CheckpointCallback(TrainerCallback):
     def on_batch_end(self, trainer: 'Trainer', **kwargs):
         current_iter = kwargs.get('current_iter')
         if current_iter - self.last_ckpt_iter >= self.checkpoint_interval:
-            trainer._save_checkpoint()
+            CheckpointCallback._save_checkpoint(trainer)
             self.last_ckpt_iter = current_iter
     
     def on_train_end(self, trainer: 'Trainer', **kwargs):
         checkpoint = cast(Checkpoint, kwargs.get('checkpoint'))
         current_iter = len(checkpoint.loss_list)
         if current_iter != self.last_ckpt_iter:
-            trainer._save_checkpoint()
+            CheckpointCallback._save_checkpoint(trainer)
 
 
 class GradientClippingCallback(TrainerCallback):
diff --git a/khaosz/trainer/trainer.py b/khaosz/trainer/trainer.py
index a2a26b6..3d44968 100644
--- a/khaosz/trainer/trainer.py
+++ b/khaosz/trainer/trainer.py
@@ -1,4 +1,3 @@
-import os
 import torch
 from typing import Optional, List
 from torch.utils.data import DataLoader, RandomSampler
@@ -29,7 +28,6 @@ class Trainer:
         )
         self.train_config = train_config
         self.schedule_config = schedule_config
-        
         self.callbacks = callbacks or self._get_default_callbacks()
         
     def _get_default_callbacks(self) -> List[TrainerCallback]:
@@ -49,19 +47,13 @@ class Trainer:
             batch_size=self.train_config.batch_size, 
             sampler=sampler
         )
-        
-    def _save_checkpoint(self):
-        current_iter = len(self.checkpoint.loss_list)
-        save_path = os.path.join(self.train_config.checkpoint_dir, f"iter_{current_iter}")
-        self.checkpoint.optim_state = self.train_config.optimizer.state_dict()
-        self.checkpoint.save(save_path)
 
     def _call_callbacks(self, method_name: str, **kwargs):
         for callback in self.callbacks:
             method = getattr(callback, method_name, None)
             if method:
                 method(self, **kwargs)
-
+        
     def train(
         self,
         train_checkpoint: Optional[Checkpoint] = None