diff --git a/phono3py/api_phono3py.py b/phono3py/api_phono3py.py
index b42d4a16..c1d8da07 100644
--- a/phono3py/api_phono3py.py
+++ b/phono3py/api_phono3py.py
@@ -58,6 +58,7 @@
 from phonopy.interface.pypolymlp import (
     PypolymlpData,
     PypolymlpParams,
+    develop_mlp_by_pypolymlp,
     develop_polymlp,
     evalulate_polymlp,
     load_polymlp,
@@ -2204,52 +2205,12 @@ def develop_mlp(
         if self._mlp_dataset is None:
             raise RuntimeError("MLP dataset is not set.")
 
-        if params is not None:
-            _params = parse_mlp_params(params)
-        else:
-            _params = params
-
-        if (
-            _params is not None
-            and _params.ntrain is not None
-            and _params.ntest is not None
-        ):
-            ntrain = _params.ntrain
-            ntest = _params.ntest
-            disps = self._mlp_dataset["displacements"]
-            forces = self._mlp_dataset["forces"]
-            energies = self._mlp_dataset["supercell_energies"]
-            train_data = PypolymlpData(
-                displacements=disps[:ntrain],
-                forces=forces[:ntrain],
-                supercell_energies=energies[:ntrain],
-            )
-            test_data = PypolymlpData(
-                displacements=disps[-ntest:],
-                forces=forces[-ntest:],
-                supercell_energies=energies[-ntest:],
-            )
-        else:
-            disps = self._mlp_dataset["displacements"]
-            forces = self._mlp_dataset["forces"]
-            energies = self._mlp_dataset["supercell_energies"]
-            n = int(len(disps) * (1 - test_size))
-            train_data = PypolymlpData(
-                displacements=disps[:n],
-                forces=forces[:n],
-                supercell_energies=energies[:n],
-            )
-            test_data = PypolymlpData(
-                displacements=disps[n:],
-                forces=forces[n:],
-                supercell_energies=energies[n:],
-            )
-        self._mlp = develop_polymlp(
+        self._mlp = develop_mlp_by_pypolymlp(
+            self._mlp_dataset,
             self._supercell,
-            train_data,
-            test_data,
-            params=_params,
-            verbose=self._log_level - 1 > 0,
+            params=params,
+            test_size=test_size,
+            log_level=self._log_level,
         )
 
     def load_mlp(self, filename: str = "phono3py.pmlp"):