During a controlled refrigeration process, even if only a refrigerating capacity obtained by an inverter compressor (32A) of a first refrigeration circuit (31A) becomes insufficient and a request for activating a constant speed compressor (32B) of a second refrigeration circuit (31B) is issued, the constant speed compressor (32B) is not immediately activated, but can be activated only by waiting until a temperature inside (TR) increases up to the upper limit temperature (TH) of a setting temperature (To). When the two compressors (32A, 32B) are in operation, even if a request for deactivatingthe constant speed compressor (32B) is issued, the constant speed compressor (32B) is not immediately deactivated, but can be deactivated only by waiting until the temperature inside (TR) drops down to a tentative lower limit temperature (TLk) that is higher than a lower limit temperature (TL) but is below the setting temperature (To) by a predetermined value.