PURPOSE: To finish injection of gas at the same time and to stir the gas effectively, by rotating a motor driving a piston at the ratio of revolving speed in proportion to the injection quantity of the gas at the time of injecting the gas in each cylinder to a gas test vessel.

CONSTITUTION: The first and the second pulse motors 11a, 11b and an exhaust pump 23 etc., are operated before injection of gas and residual gas in piping is exhausted. Suction valves 4a, 4b are then opened and the gas is supplied to each cylinder 6a, 6b. On occasion of injecting the gas, when the quantity of injecting gas is e.g. 80cc and 20cc, the injection is carried out by rotating the motors 11a, 11b at the ratio of 80:20 revolving speed. This cycle is repeated until the set total gas quantity is detected. For this reason, the injection to a test vessel 20 of both gases is finished at the same time and the injected gas in the vessel is stirred effectively.