PURPOSE: To enable an amount of fluorocarbon liquid within a final recovery tank to be acknowledged from outside without applying any special machining work to the final recovery tank by a method wherein a liquid sensor is arranged at a mean pressure pipe for releasing a pressure corresponding to a volume of liquified fluorocarbon supplied to a final recovery tank.

CONSTITUTION: Gaseous fluorocarbon taken out of a second outlet 16b of a primary recovery tank 16 is supplied to a condensing device 18b of a two-system heat exchanger 18 through a pipe 12. In this case, the gaseous fluorocarbon is cooled and liquified under a thermal absorbing action at an evaporating system 18a. The liquified fluorocarbon is recovered to a final recovery tank 19 through a pipe 12. A condensing side 18b of the two-system heat exchanger 18 and the final recovery tank 19 are connected by a mean pressure pipe 20. A pressure within the take is increased by an amount corresponding to a volume of liquified fluorocarbon. However, this pressure is released through the mean pressure pipe 12 and the pressure within the final recovery tank is always kept at a substantial constant value. The fluorocarbon liquid ascending within the mean pressure pipe is detected by a liquid sensing means 21 arranged in the means pressure pipe.