To smoothly start a compressor used in an air conditioner regardless of environment conditions and load conditions and inhibit sounds and vibrations during the start.

When a motor 7 is started, a microcomputer 17 sets a start control amount of the motor 7 on the basis of at least one information of a coolant temperature of a compressor 9 and a restart time interval of the compressor 9. As the start control amount, a start current command, a maximum rotation speed command, and a rotation speed acceleration rate command are used. When the coolant temperature and the restart time interval are normal values, the setting of the start control amount is not changed. However, when one of the coolant temperature and the restart time interval deviates from the normal value, a start current is increased, a maximum rotation speed is increased, and a rotation speed acceleration rate is decreased.