PURPOSE: To reduce the capacity and to promote the efficiency of an accumulator by introducing the refrigerant condensed and liquefied in an evaporator under a defrosting operation into another evaporator under a cooling operation as cooling refrigerant.

CONSTITUTION: There are provided bypass pipe passage 24A--24C and 25, nonreturn valves 21A- -21C, switch valves 22A--22C, and reducing nonreturn valves 26A--26C. In this consturction, when a cooling unit A is given a defrosting operation, an electromagnetic valve 12A given the instruction of a defrosting timer is closed, and an evaporator 14A is intercepted from the supply of refrigerant to be filled with gas-shaped refrigerant of a low pressure. Then, an electromagnetic valve 23A is closed, and electromagnetic valves 20A and 22A are opened. The gas-shaped refrigerant of a high temperature and pressure running in a hot-gas pipe passage 19 is introduced into the evaporator 14A to be condensed and liquefied after defrosting. Furthermore, the refrigerant is introduced into bypass pipe passages 24B and 24C in cooling units B and C under a cooling operation through bypass pipe passages 24A and 25, decompressed in reducing nonreturn valves 26B and 26C, made to join into the liquefied refrigerant from a high pressure refrigerant pipe passage 11, introduced into evaporators 14B and 14C, and runs in a refrigerant circuit as refrigernat.