To prevent a voltage on the boost side from being varied due to synchronization with a current to be made to flow to a phase with no current sensor mounted thereon out of three phases of a three-phase AC electric motor.

A drive unit determines one of the following states: an in-phase synchronization state in which a change in voltage on the boost side and a change in current command of a W-phase are synchronized with each other substantially in phase; an opposite-phase synchronization state in which both changes are synchronized with each other substantially in opposite phase; and a third state that is not in-phase synchronization state nor the opposite-phase synchronization state. The drive unit sets a base value α1 as an offset correction value α when an amplitude of the change in the voltage on the boost side is smaller than a predetermined value, and also when the amplitude is not smaller than the predetermined value and the drive unit is in the third state. The drive unit sets a value (α1-α2) as an offset correction value α when the amplitude is not smaller than the predetermined value and the drive unit is in the in-phase synchronization state. The drive unit sets a value (α1+α2) as the offset correction value α when the amplitude is not smaller than the prescribed value and the drive unit in the opposite synchronization state. Then, the drive unit controls an inverter by using corrected phase currents Iu, Iv obtained by correcting detection phase currents Iua, Iva by using the offset correction value α.