PURPOSE: To prevent the generation of an accident by a method wherein a combination of gases not having to be mixed is preset and, during a time when one gas is introduced into the system, the opening of the introducing valve of the other gas is prohibited.

CONSTITUTION: The manifold 6 connected to several kinds of gas sources through introducing valves 1W5, a pressure detection means (a) detecting the pressure in the system containing the manifold 6 and an exhaust means (b) evacuating the system are provided to measure the gas adsorbing quantity of the specimen W in a specimen container 7. A system introduced gas memory means (c) stores the kind of the gas introduced into the manifold 6 when the introducing valves 1W5 are opened. A discrimination means (d) discriminates the kind of gas not having to be introduced on the basis of the content of the means (c) and the pressure in the system by the means (a), and an interlock means (e) prohibits the opening of the introducing valve concerned on the basis of the result of discrimination. By this method, the introduction of preset gas is automatically prevented until the pressure in the system reaches a predetermined value or less so as to prohibit the mixing with respect to the gas introduced into the system.