PURPOSE: To immediately execute the adjustment of supplying pressure of a gas by a method wherein a specimen gas is measured at a plurality of predetermined carrier gas-supplying pressures to obtain a relationship between the carrier gas supplying pressures and maintaining time periods and the carrier gas pressure of which maintaining time period becomes constant by virtue of the specimen gas is calculated in accordance with the relationship.

CONSTITUTION: In a carrier pressure adjustment section 9, a carrier pressure P1 greater than a desired carrier pressure and a carrier pressure P2 lower than the desired carrier pressure are prepared, a pressure reducing valve 1 of a pressure reducing control section 3 is controlled so that the carrier pressures are set to the pressures P1, P2. After the carrier pressures P1, P2 are normalized, an analyzer valve 4 is driven by the adjustment section 9, then a prescribed quantity of the specimen gas is introduced into a column 5 and a peak representation times Rt1, Rt2 of the specimen gas by the carrier pressures P1, P2 are stored in a memory. Next, the desired carrier pressure Psp is obtained in accordance with an equation of Psp=(Rtsp-Rt1)×(P2-P1)/(Rt2-Rt1)+P1. Rtsp is a center of a band of gate time determined by a component of the specimen gas. The adjustment section 9 sets the carrier pressure Psp to a control section 8.