PURPOSE: To enhance the universality of the titled apparatus, by a method wherein a constant flow amount valve and a pressure regulating valve or a needle valve different in characteristics are combined and the selective use thereof is performed before and after specimen injecting operation.

CONSTITUTION: At the begining of specimen injecting operation, a flowline change-over device 2 is rotated 90° and a carrier gas is flowed through an equivalently adjusted variable register 7 to make the outlet pressure of a constant flow amount valve 1 unchangeable. The carrier gas passing a pressure regulating valve is flowed to the direction of a capillary column 4 through a specimen injecting apparatus 3. That is, when a needle is passed after a needle guide is pierced in order to pierce a syringe through thin septum rubber at the beginning of injecting operation, the carrier gas is leaked from the periphery of the needle and the inlet pressure of the capillary column is made almost equal to the atmospheric pressure. In the next step, this leakage is stopped and, when the indication of a pressure gauge 8 is raised to be made equal to the indication of a pressure gauge 5, the flowline change-over device 2 is returned to the original. Subsequently, the plunger of the syringe is pushed to put a specimen on a place in the vicinity of the inlet of the capillary column 4 and retracted to pull out the needle from the septum rubber. Thereby, measurement is performed smoothly.