PURPOSE: To obtain a marked circulator which provides the effective reuse of inert gas by forming a circuit for inert gas and then by providing this circuit with a cooler, trap and cylinder through a compressor.

CONSTITUTION: At the operation start of furnace 1, inert gas supplied from cylinder 8 fills furnace 1 and circulating passage 4. Next, compressor 5 is driven, following up the operation of furnace 1, to discharge the inert gas from furnace 1 through passage 7. The exhaust gas is cooled to a degree that compressor 5, etc., are not hindered, impurities such as vapor in the gas the removed by trap 16, and compressor 5 applies pressure into furnace 1 through supply passage 6. When inert gas is excessive in operation, pressure gauge 18 detects it and compressure 5 applies pressure to open solenoid 23, thereby collecting and storing it in cylinder 8.