A motor is provided with an insert nut 10 that has a knurled part 101 at two places on the surface thereof along an axial direction thereof with projections 103 for whirl stop and slip-off stop formed on the knurled part, and that is embedded between the motor rotor 3 and the magnet assembly 7 to perform fastening between the motor rotor 3 and the magnet assembly 7, and in the insert nut 10, a concave part 104 between the knurled parts 101 is situated at a mounting boundary between the motor rotor 3 and the magnet assembly 7.