A control apparatus for a vehicle controls the input power of an AC motor to reduce the difference between a target value and detected value of the system voltage. When a rotation speed of the AC motor increases to be higher than a predetermined value or when a command value of a torque generated by the AC motor increases to be greater than a predetermined value, a current vector is adjusted to a value on a lagging side in order to control the input power of the AC motor. Thus, an input power operation quantity required for stabilizing the system voltage can be realized with a high degree of reliability. When the rotation speed and the command value decrease, the current vector is adjusted to a value on a leading side in order to control the input power of the AC motor.