Control device of AC motor

A control device of a three-phase AC motor includes: an inverter; a current sensor for a sensor phase current; and a controller switching a switching element of each phase of the inverter and having a current estimation device, which calculates a sensor-phase-standard current phase according to α and axis currents and a current estimated value of another phase. The current estimation device calculates the α axis current at every switching and intermediate timings, calculates a first differential value of the α axis current at every switch timing, calculates the axis current according to the first differential value, calculates a second differential value of the α axis current at every intermediate timing, and calculates the axis current according to the second differential value. The intermediate timing is set to have an unequal interval between two adjacent switch timings.