PURPOSE: To easily prevent the generation of breaks and cracks and improve yield and productivity by providing the cuttings to the outer most ridge of the opposing surface of core.

CONSTITUTION: The grooves 1, 2 for embedding coil are formed at the time of forming a ferrite core and simultaneously a stepped portion 7 is formed at the outermost ridge of opposing surface. This stepped portion 7 is provided at the grinding part 6 to be ground during grinding of core and is perfectly removed by the grinding. Therefore, as the final core 5, the core the same as the conventional one can be obtained. Thereby, breaks and cracks of core due to mutual collision of cores can be prevented during manufacture of cores. Moreover, the cuttings provided to the outermost ridge of the opposing surface of core is not limited only to the stepped portion but may be formed in the shape of inclined surfaces 8 and 9.