Control mode switching determination is made as a part of a main loop (control period for overall control of an AC electric motor. When switching from the rectangular wave voltage control mode to PWM control mode is determined, the change in voltage phase of the rectangular wave voltage is inhibited from the timing of control mode switching determination until the next execution of the main loop until the timing at which the control mode is actually switched, to maintain voltage phase of the rectangular wave voltage at the time of control mode switching determination. Consequently, in a drive controller for an AC electric motor allowing switching between control modes, control mode can appropriately be switched without destabilizing the operation of the AC electric motor.