PURPOSE: To know the timing required for the regeneration of a cryopump correctly by providing a means to correct the integrated value substantially in accordance with the supply amt. and kind of the gas into a chamber to be exhausted.

CONSTITUTION: A signal corresponding to argon gas is fed to an arithmetic circuit 12 from a gas feed control circuit 11, and a factor is multiplied to the pressure signal from a vacuum gauge in accordance with the signal from the gas feed control circuit 11. Said factor is changed depending on the type of gas introduced into a chamber 1 to be exhausted. When the integrated value by an integrator 13 becomes the preset value or more corresponding to the critical gas molecular weight for a pump preset beforehand in a control circuit 15, the control circuit 15 closes a valve 3 and also stops the operation of the pump 4.