A low speed region position estimating portion is designed to be suitable for when the motor is operating in a low speed region, and estimates a low speed estimated rotational position θ^L. A high speed region position estimating portion is designed to be suitable for when the motor is operating in a high speed region, and estimates a high speed estimated rotational position θ^H. A dividing portion obtains a divided estimated rotational position θ^M by internally dividing the low speed estimated rotational position θ^L and the high speed estimated rotational position θ^H. A rotation speed calculating portion obtains a rotation speed ω of a rotor based on an output signal from a steering sensor. The rotational position of the rotor is then obtained by selecting one of i) the low speed estimated rotational position θ^L, the high speed estimated rotational position θ^H, or the divided estimated rotational position θ^M, based on that rotation speed ω.