To effectively utilize a working fluid to improve refrigeration capacities by fluidly connecting a buffer tank to a high temperature end of a pulse tube through a passage open/closure valve and fluidly connecting the buffer tank to a compressor unit through a passage switching valve so as to be switched to a high pressure port or a low pressure port of the unit.

A buffer tank 23 is provided at the top end of a pulse tube 1 so as to communicate therewith through a passage open/closure valve 22 formed from motor-operated rotary valve. The top end of the tank 23 is fluidly connected to a high pressure gas passage 14 and a low pressure gas return passage 15 of the unit 5 through an auxiliary passage switching valve 24 formed from a motor-operated rotary valve. With this arrangement, high pressure gas from a compressor 1 is fed into the pulse tube 1 through the tank 23 to return a part of gas in the tube 1 to the compressor 7 through the tank 23. As a result, width of pressure variation in the tube 1 can be increased so that refrigeration capacities of a refrigerator can be improved.