A motor drive apparatus receiving power from a power source and driving a motor with independent polyphase systems of excitation coils, comprises: a control circuit and power converters each corresponding to one system, each including an inverter circuit, an interrupter circuit, and a temperature detector, the inverter circuits being connected in series to the power source and, while not short-circuited, supplying power to the excitation coil, wherein the control circuit detects an operating state of the motor, short-circuits the inverter circuits and interrupts the interrupter circuits for a subset of power converters defined according to the operating state, such that a source voltage is supplied to non-short-circuited inverter circuits, and, when a power converter exceeds a predetermined temperature, the control circuit short-circuits the inverter circuit and interrupts the interrupter circuit thereof, and, in another power converter not exceeding the predetermined temperature, operates the inverter circuit and connects the interrupter circuit.