PURPOSE: To carry out high precision and high reliability inspection by filling helium in a refrigerant flow passage and detecting helium gas leak.

CONSTITUTION: An inspected object 16 in the refrigerant passage of which helium gas is filled under pressure prior to inspection is placed in a tightly closed chamber 14, the valve of a pre-exhausting system 19 is opened and pre-exhausted to a specified pressure P2. Next, the valve of a pretest exhausting system 20 is opened and vacuum-exhausted so as to maintain near the pressure P2, a part of the exhausted gas is introduced to a helium gas detector and pretested. When gas is not detected, the valve 25 of a main exhausting system 21 is opened to pump down the inside of the closed chamber 14 to a pressure P3, then the valve 26 of a main exhausting system 22 is opened and vacuum exhausting is continued to keep the pressure inside almost at P3 and a part of the exhaust gas is introduced to the helium gas detector for main test.