To reduce noise and improve efficiency with sinusoidal drive by calculating a phase according to the specific single output of a plurality of position sensors or entire output, when the fluctuation of a time interval is at a prescribed value or smaller, or at a prescribed value or larger.

Constant-speed mode or acceleration/deceleration mode determination is made from a position sensor mounted to a U phase, for example, in mode determination 19. Phase operation 17 calculates a phase θ of the induced voltage of U phase, according to the output signal of a position sensor 20 based on the determination result of the mode determination 19. For example, Hu, Hv, and Hw indicate a position detection signal that is the output signal of a Hall IC. The mode determination 19 measures the signal interval of Hu and determines that the mode is the constant-speed mode and the acceleration/ deceleration mode when the change in the signal interval is equal to a prescribed value or less, and equal to a prescribed value or more, respectively. A phase operation means 17 calculates the phase based on the mode determination. More specifically, only one position sensor and all signals are used at a constant speed and acceleration modes, respectively, thus reducing the deviation between an operation phase and an actual phase.