An overmodulation PWM controller includes: a voltage instruction calculation unit which calculates a d-axis voltage instruction and a q-axis voltage instruction in which a voltage amplitude exceeds a peak value of a triangular wave carrier; a voltage instruction correction unit which corrects the d-axis voltage instruction and the q-axis voltage instruction so that a pulse width modulation voltage applied to an AC motor has a basic wave amplitude based on the voltage instruction amplitude, according to the synchronization value K which is the number of the triangular carriers per one cycle ofthe phase voltage instruction; and a voltage instruction conversion unit which converts the corrected d-axis voltage instruction and the q-axis voltage instruction into a phase voltage instruction. The pulse width modulation voltage is controlled according to the result of comparison between the phase voltage instruction and the triangular wave carrier.