PURPOSE: To eliminate that air bubbles are generated in a solvent and to stably deliver a liquid by a method wherein a damper in which a fluid whose volume compression rate is larger than that of a mobile phase has been sealed is installed on the upstream side of an entrance-side check valve.

CONSTITUTION: A damper 20 is interposed between a low-pressure deareation device 11 and a plunger pump 12. Thereby, the air which has been sealed inside a gas chamber 33 in the damper 20 is expanded immediately at the point of time when the pump 12 starts a suction process, and a solvent 17 inside a solvent chamber 32 is supplied immediately to the pump 12. Consequently, the pressure of the solvent 17 inside the pump 12 is not lowered. As a result, even when the solvent 17 having a low boiling point or the solvent 17 having a high viscosity is used, air bubbles are not generated inside the pump 12. Thereby, when the suction process of the pump 12 has been stabilized or after a discharge process is started due to the viscosity of the solvent 17, the solvent 17 in a reserve 10 is supplied to the solvent chamber 32 in the damper 20 through the device 11, and the air inside the gas chamber 33 is compressed and returned to its original pressure.