A rotational angle correction controller controls generation of an inverse assist torque using the “phase deviation” due to the correction of the rotational angle θ, thereby performing the rotational angle correction control to smooth rotation of the motor during two phase drive. In addition, the rotational angle correction controller includes an oscillation detection part that detects the occurrence of oscillation in the steering system. When the level of the detected oscillation exceeds the predetermined level, the correction amount in the rotational angle correction control is reduced.
