To effectually return staying refrigerator oil in a refrigerator using the oil having bad compatibility with an HFC refrigerant for eliminate the possibility that the oil might be separated and stay in an evaporator and hence oil of a compressor might run out.

The present structure is adapted such that a cross section of a refrigerant piping 13 of a heat exchanger 15 constituting an evaporator 1 is formed into a gourd shape, and a heater 23 is mounted on an outside lower surface of a gourd shaped lower room 21. With the guard shape of the cross section, refrigerator oil 25 staying in the lower room 21 is effectively heated and evaporated with the heater 23, and is returned to a compressor together with refrigerant gas. Otherwise, an oil guide pipe is provided, on the U-bent part of the refrigerant piping 13, and is connected with a downstream refrigerant piping of the compressor through a solenoid valve opened only upon starting of the compressor.