A control apparatus controls an AC motor by detecting current passing through one phase. The apparatus includes an upper controller which includes a torque command calculation section, and a torque monitoring section monitoring torque to determine whether the torque is within a range, and a lower controller which controls current supply to an inverter based on a torque command value to control the motor, and which acquires information on a current-supply state and a rotation state of the motor and transmits information on a control state to the upper controller. At least one of the controllers estimates a current estimate value of an estimated phase or a d-q axis current estimate value based on a current detection value of the one phase and an electrical angle, and calculates information for monitoring torque based on the current estimate value. The torque monitoring section monitors the torque based on the information.