A motor drive according to the present invention has a dynamic braking circuit. The motor drive includes a motor drive control circuit for applying a voltage to windings of a synchronous motor and the dynamic braking circuit for a predetermined time by switching power transistors connected to a direct current power supply, a current detection circuit for detecting a current value outputted from the power transistor, and a failure determination circuit for determining the presence or absence of a failure in the dynamic braking circuit from the current value detected by the current detection circuit and a predetermined threshold value. When the presence or absence of a failure in the dynamic braking circuit is detected, the resistance of the dynamic braking circuit is changed.