When a lock detector detects a locked state of a DC motor in a starting stage, a torque increasing circuit immediately selects a starting sequence pattern of an output torque that is greater in magnitude by one preselected step, and outputs the selected output torque to a starting sequence controller, so that a compressor can be restarted speedily without repeating starting failures. A compressor, driven by a DC motor, has a shell of an internal pressure approximately equal to the pressure of an inhalation gas. An inverter is provided to make the speed of the DC motor variable. A rotational frequency setting circuit sets the rotational frequency of the DC motor to a frequency that is not greater than the frequency of a commercial power source when the internal temperature of a refrigerator is stabilized. By this construction, the power consumption can be remarkably reduced.