PURPOSE: To easily fit various mechanisms in a wheel motor in which an electric motor is built in the wheel of a tire by providing a disc shaped rotor rotating in one body with the tire, and providing a brake caliper sandwiching the disc shaped rotor as a brake disc.

CONSTITUTION: The center part of a rotor disc 1 is fitted to a fixed member 3 through a bearing 2. A brush 5 is arranged on one end of the rotor disc 1. An electromagnet 6 composed of a coil 6a and a yoke 6b is arranged on the outer circumference of the rotor disc 1, and also a brake caliper 7 and another brush 8 are arranged thereon. The rotor disc 1 is insulated from the outside through a plurality of insulating bodies 4, 9, 14, and connected to a tire 11 through a wheel rim 12. When voltage is impressed between the respective brushes 5, 8 at this time, the magnetic flux due to the electromagnet 6 passes so as to rotate the rotor disc 1. Consequently a disc brake is constituted of the rotor disc 1 and the brake caliper 7.