PURPOSE: To prevent the frosting over an evaporator as the consumption power of a freezing unit is prevented from exceeding a set value by providing a means to detect the consumption power of the freezing unit and a controller to switch an evaporator fan to low speed operation when the detected power attains a set value.

CONSTITUTION: The consumption power of a freezing unit is detected by means of a power detecting means 50. A detected value P is inputted to a comparing means 52 of a controller 51, and the detected value is compared with a set value PS, inputted from 8 set means 53, thereby. When the detected value P attains the set value PS, the comparing means 52 outputs it to a switching means 54, and the switching means 54 switches an evaporator fan 12 to low speed operation by switching the tap of a fan motor 11 to the lower speed side. This constitution prevents the occurrence of frosting to an evaporator as the consumption power of the freezing unit is prevented from exceeding a set value. Further, freezing capacity can be improved.