Electric power steering system

An electric power steering system is provided, which employs an electric motor (M) as a drive source to apply a steering assist force to a steering mechanism (3) mounted on a motor vehicle in accordance with the operation of an operation member. The electric power steering system includes: a torque sensor (5) which detects a steering torque applied to the operation member (1) and outputs a torque signal in accordance with the detected steering torque; and a motor driving control circuit (14; 70, S4, S14) which outputs a motor driving command signal for driving the electric motor (M) on the basis of the torque signal outputted from the torque sensor (5). At start or stop of the operation of the electric power steering system, the motor driving command signal is limited in accordance with the magnitude of the steering torque detected by the torque sensor (5) (12, 21; 70, S5, S15).