Abstract: A motor drive device includes: an inverter unit that supplies alternating current to a motor including a plurality of stator windings; a connection switching unit that is disposed between the inverter unit and the motor and switches a connection state of the stator windings; a rotor flux estimation unit that calculates an estimated rotor flux that is an estimated value of a rotor flux of the motor on the basis of current information that is a result of detection of a current value of the alternating current; and a determination processing unit that determines the connection state on the basis of the estimated rotor flux. The motor drive device determines an anomaly of the connection state while the motor is in operation.