PURPOSE: To simplify maintenance of vacuum tank while reducing power consumption by providing a connecting circuit for supplying high temperature refrigerant gas to the circuit connecting a first heat exchanger and a third gate valve, and providing the connecting circuit with a heater for heating high temperature refrigerant flowing through the connecting circuit.

CONSTITUTION: Since an article to be frozen/dried can be heated by supplying high temperature refrigerant gas compressed by a refrigerator 8 through a direction switching valve 20 to a first heat exchanger 12 and the temperature of the refrigerant gas can be increased by providing a connecting circuit 24 for supplying refrigerant gas from the direction switching valve 20 to the first heat exchanger 12 with a heater 9, no electric heater is required in a vacuum tank 1 and manufacture and maintenance thereof are facilitated. Furthermore, a cold trap 6 can be operated with no trouble at the time of heating because a third gate valve 22 and a feedback circuit 27 are provided.