A parking brake actuator generates and applies a braking force to a vehicle wheel by converting a rotation movement of a screw member which is rotated by an electric parking brake driving device into a translatory movement and transmitting the converted translatory movement to a piston to push a brake pad to a disc by the piston. The electric parking brake driving device includes an electric motor and a reduction gear mechanism which transmits the driving force of the electric motor to the electric parking brake driving device. The reduction gear mechanism includes a pinion gear fixed to an output shaft of the electric motor, a first gear shaft rotatably supported on a first bearing member provided on a gear body and a first wheel gear formed on the first gear shaft and engaging the first wheel gear to thereby reduce the speed of driving force of the electric motor.