A controller includes: an inverter having switching devices for converting by a PWM method and supplying an electric power to a multi-phase rotary device; a duty calculator calculating a duty command value with To; a pseudo duty calculator calculating a N-th update duty value based on N-th and (N−1)-th duty command values according to a ratio of To/Tr with a linear compensation method; a comparator comparing the update duty value with a carrier wave to generate an on-off signal of each switching device; and a detector detecting current of each phase with To. The duty calculator changes an average voltage of each phase to make an on-state time of a detection side switching device equal to or longer than minimum. When the on-state time at one phase is smaller than minimum, the pseudo duty calculator outputs a pseudo duty value to detect the current of other phases.