PURPOSE: To improve design freedom, by arranging an armature core formed by overlapping two semiarcuate cores splitted in axial direction at one radial outside of rotor while facing therewith, thereby providing a portion where the armature core does not exist at radial outside of rotor.

CONSTITUTION: A rotor magnet 20 is fixed to a shaft 15 so as to form a rotor 14, then an armature core 26 is arranged through a radial gap at the outer circumferential side so as to form a radial gap type motor. The armature core 26 is formed by overlapping two semiarcuate cores 24, 25 two in axial direction of the rotor 14, and arranged only at one outside of the rotor 14. Since other part 35 can be arranged in a space outside of the rotor 14 where the armature core 26 does not exist, design freedom of machine incorporating a motor can be improved.