The controller estimates torque output by the motor and controls the current supplied to the motor in such a manner that a torque estimate of the motor obtained by the estimation corresponds to the torque command value. A torque estimation calculator 120 estimates the torque output by the motor. A phase error command calculator 125 calculates a command value of a phase error from the deviation between the torque estimate and a torque command value. A speed estimation calculator 130 outputs a speed estimate in such a manner that a phase error estimate corresponds to the command value of the phase error.