A motor controller for controlling a permanent magnet motor having a rotor having a permanent magnet and a stator having multiphase windings including a position detector generating and outputting rotor rotational position signal; a waveform data storage storing sinusoidal waveform data; a drive signal output section reading the waveform data from the waveform data storage at timings determined based on the rotational position signal and outputting a voltage signal corresponding to the waveform data to the windings through a drive section; a data history storage storing data corresponding to the voltage signal of previous control period; and an output data modifier that, when outputting the voltage signal in current control period, compares corresponding waveform data with previous waveform data, and if difference between the current and the previous data is equal to or greater than a predetermined value, current output data is modified by a portion of the difference.