PURPOSE: To precisely control the flow amount of generated stock gas even in a small flow amount, by a method wherein a gaseous mixture is branched into two streams at the outlet of an output arranged pipe and a second gas flow controller is provided to one of branched arranged pipes while a gas resistance means is provided to the other branched arranged pipe.

CONSTITUTION: The outlet of carrier gas is branched by a branching device 20 and second flow controller 21 similar to a first flow controller 11 is provided to one of branched pipes while a gas resistance means 23 for imparting resistance to a gas flow amount is provided to the other branched pipe and taken out from an outlet 22. Stock gas of which the flow amount is regulated by the second gas flow amount controller 21 is sent out from the outlet 22 and the residue in the stock gas which is generated in a bubbler 12 and issued from the outlet 22 is taken out from an outlet 24 through the gas resistance means 23.