Provided is a control device for a synchronous motor, the control device including a DC excitation command generation unit which generates a command for sending a DC current with a fixed current phase to a synchronous motor, and controls the magnitude of the DC current so as to apply deceleration torque to a rotor of the synchronous motor on the basis of at least one among the angular acceleration and the angular velocity of the rotor; and a magnetic pole position acquisition unit that acquires, as information indicating the magnetic pole position, the angular position of the rotor based on the output signal when a predetermined detection end condition is satisfied.