A motor controller includes an output voltage modulator that outputs sinusoidally-modulated voltage for driving a motor; a modulation factor specifier allowing specification of a modulation factor greater than 1.0 for the output voltage; a current detector that detects current flowing in the motor; and a field-oriented controller that divides the current detected by the current detector into a d-axis current component and a q-axis current component and that conforms each of the components to a command current produced based on a command rotational speed; a rotational position estimator that estimates motor rotational speed and rotor rotational position for use by the field-oriented controller; wherein the position estimator includes a filter that smoothes a d-axis induced voltage obtained during the estimation, and the motor rotational speed and the rotor rotational position are estimated based on the d-axis induced voltage smoothed by the filter.