To provide an electric power steering system excellent in steering feeling, for generating assist torque of an electric motor without delay in start of steering from a steering neutral state.

A correction amount setting part 21 sets a correction amount Ia to satisfy the equation Ia=Ksin(wt), when steering torque T which is detected by a torque sensor 13 is within a predetermined range (-T1≤T≤T1), where, the K is a constant. The correction amount Ia is added to a control valve I which is set by a control value setting part 20 to correct a control value I. In the steering neutral state, the control value I for the electric motor 16 is periodically fluctuated at minute amplitude to make the electric motor 16 in a warm-up state. Therefore, the assist torque of the electric motor 16 can be generated without delay in the start of the steering from the steering neutral state.