A control device for a three-phase alternate current motor includes: a control phase current acquisition means; a monitor phase current acquisition means; a rotation angle acquisition means; a two-phase control current value calculation means; a one-phase current estimated value estimation means; a voltage command value calculation means; an other phase current estimation means for calculating a monitor or a control phase current estimated value; an abnormality detection means for detecting an abnormality in a monitor phase or a control phase current sensor; a number-of-revolutions calculation means for the motor; a number-of-revolutions determination means for determining whether the number of revolutions is not larger than a predetermined determination value; and a switching means between a two-phase control mode when the number of revolutions is not larger than the determination value and a one-phase control mode when the number of revolutions is larger than the determination value.