PURPOSE: To make it possible to remove both solvents supplied from a jet separator and a capillary column, by providing a specimen introducing line opening and closing means in an ion source.

CONSTITUTION: A jet separator 12 is communicated with the ionization chamber 16 of an ion source 14 by a pipe 20 and a capillary column 18 is communicated with the ionization chamber 16 by pipes 22, 20 while a solvent removing valve 26 is arranged to the specimen introducing line 24 in the ion source 14. When the specimen contained in a solvent is discharged from a gas chromatograph 10, said solvent is supplied to the jet separator 12 through a pipe 28 and supplied to the pipe 20 while the mixing ratio with carrier gas becomes large. At this time, when the specimen introducing line 24 is closed by the valve 26, the solvent is sufficiently removed. When the valve 26 is opened thereafter, a specimen long in a holding time is supplied to the ionization chamber 16 to make it possible to perform mass analysis. Even when the solvent is supplied through the pipe 22, the solvent is sufficiently removed in a similar way by the operation of the valve 26 to make it possible to perform mass analysis.