GAS CHROMATOGRAPH

PROBLEM TO BE SOLVED: To provide a GC capable of simply monitoring a primary pressure without adding a pressure sensor and accurately calculating a flow rate. SOLUTION: First, when a power source is turned on, a port Common is connected to a port Normal Close of a three-way solenoid valve SV. Then, the primary pressure is monitored by the pressure sensor S2. Then, the port Common is connected to a port Normal Open, and a carrier gas of a predetermined flow rate is supplied to a sample vaporizing chamber. Then, the flow rate is calculated by using a monitored value of the primary pressure of the sensor S2 and a monitored value of a differential pressure sensor S1. The flow rate is fed back to control a flow rate of a flow control valve V1. Simultaneously, a monitored value of the sensor S2 communicating with a septum purging channel 4 is read. Thus, the pressure in the vaporizing chamber 21 is held constantly by a flow control valve V2. The sample is injected in a sample vaporizing chamber 1 by a sample syringe (not shown) in this state.