A motor control signal output unit of an electric power steering system includes a feedback gain calculation unit (52), and a feedback control unit executes a feedback control with the use of a proportional gain (Kp) and an integral gain (Ki) that are calculated by the feedback gain calculation unit (52). The feedback gain calculation unit (52) sets the feedback gains to large values (Kp=P0, Ki=I0) when the absolute value of an assist gradient (α) is equal to or smaller than a predetermined value (α0) (|α|≦α0). On the other hand, when the absolute value of the assist gradient (α) exceeds the predetermined value (α0) (|α|>α0), the feedback gain calculation unit (52) sets the feedback gains to small values (Kp=p1, Ki=I1:P1