To provide a motor drive device for a compressor that suppresses a regeneration phenomenon when a compressor motor in an air conditioner stops, and eliminates an increase of cost resulting from the high-pressure resistance of a smoothing capacitor.

The motor drive device for the compressor includes a phase shifting means 6 which can freely be inserted and extracted between an inverter circuit 5 and the smoothing capacitor 3. When stopping the compressor motor 20, an inverter control means 10 detects phases of a current and a voltage of a winding of the compressor motor 20, and when the phases of the current and the voltage differ from each other, the phase shifting means 6 is inserted between the inverter circuit and the smoothing capacitor. When the phases of the current and the voltage coincide with each other, a signal is generated which turns on/off an element of the inverter circuit 5 according to the direction of the current which is detected by a current detection means 4, and flows in the winding of the compressor motor 20.