PURPOSE: To enable stable operation of a cryogenic apparatus without relying on changes in heat load under a heat shielding by adjusting the temperature of a return working gas from an object to be cooled to the optimum control allowable temperature of a cold box.

CONSTITUTION: The temperature of a return gas from a 40 K shield line 10 is regulated to a fixed value (the optimum control allowable temperature of a cold box) by a flow control valve 6, a heater 13 and a TIC controller 15 with respect to a change in the heat load of a 40 K shield as heat shield of an object 8 to be cooled. This temperature regulation enables obtaining of a stable refrigerating capacity without disturbing the temperature balance in the cold box 9. In short, this enables stable operation of a helium liquefied refrigerating unit.