To obtain the operation controller for a cooling cycle using a DC motor which starts the DC motor, after the demagnetization limit current of the rotor of the DC motor is increased.

This controller is provided with a cooling cycle 2, a stator 7 and a rotor 8 which a DC motor 6 comprises an inverter device 12 which controls the revolution of the DC motor 6, a microcomputer 16 which is provided in the inverter device 12 and outputs the rotation command of the DC motor, a chopping signal generating means incorporated in the microcomputer 16, a synthesizing means and a semiconductor switch drive means which drives a semiconductor switch, are provided. Demagnetization limit current of the rotor 8 can be increased, and the probability of the demagnetization of the rotor, which is caused by a peak current when the DC motor is started under abnormal operation conditions such as the operation of the cooling cycle 2 under a low environmental temperature, etc., can be reduced.