PURPOSE: To provide an operating method for working out a safety countermeasure such as preventing hydrogen from exploding even when a temperature rises of a cryopump at its regeneration or operation time.

CONSTITUTION: In the case of detaching combustible gas 3 adsorbed to an adsorbing fin 2 in a cryopump 1, so that a proportion of forming mixed gas 5 of the combustible gas 3 with diluting inert gas 4 is provided out of the exploding limit of the mixed gas 5 and air, the cryopump 1 is operated so as to introduce the inert gas 4 into the cryopump 1.