To reduce noise of an engine and a compressor by a method wherein an operation of an engine is changed over to a low speed operation when a deviation of an outdoor temperature from a set outdoor temperature is a predetermined value or lower.

A detected temperature of an outdoor temperature sensor 31 is inputted to a high speed and a low speed determining means 40, a set outdoor temperature set by an outdoor temperature setting means 45 arranged at a control device 60 is inputted to a high speed and low speed determining means 40 through a switch 45a and at the same time an in-refrigerator set temperature set by an in-refrigerator temperature setting means 46 is inputted to the high speed and low speed determining means 40 through a switch 46a. Then, the high speed and low speed determining means 40 changes over an operation of an engine to a low speed operation when a deviation of an outdoor temperature detected by the outdoor temperature sensor 31 from a set outdoor temperature set by an outdoor temperature setting means 45 is a predetermined value or lower in the case that the switch 45a is closed. Accordingly, it is possible to reduce noise of the engine and the compressor.