A brake structure for a wheel rotating device is disclosed, which comprises a motor provided in a wheel and is driven for rotating the wheel, and a braking mechanism for actuating brake to brake the wheel. The motor includes: a motor housing; a stator positioned in and fixed to the motor housing; and a rotor positioned in the motor housing and facing to the stator. The braking mechanism includes: a brake rotor to rotate with the wheel; frictional members to be in contact with the brake rotor for generation of braking force; a pressing force generating unit for generating pressing force of the frictional members so that the frictional members are urged to and pressed against the brake rotor by supplying brake fluid through a brake fluid passage to transmit fluid pressure; and a housing for the pressing force generating unit. The brake fluid passage is formed inside a wall of the motor housing, and is connected to a brake fluid supply port provided in the housing for the pressing force generating unit.