A control device 1 for a synchronous electric motor that switches a drive control of the synchronous electric motor to a PWM drive control and a rectangular wave drive control includes a PWM signal generator 14 configured to generate a PWM signal, a rectangular wave signal generator 22 configured to generate a rectangular wave signal, a rotation speed detector 40 configured to detect a rotation speed of the motor 2, a signal switching determination part 50 configured to determine, according to at least the rotation speed, whether the PWM signal or the rectangular wave signal is used as a control signal when controlling the drive of the motor 2, and a drive controller 30 configured to control the drive of the motor 2 using a signal determined by the signal switching determination part 50 to be used as the control signal.