To supply liquid of normally constant volume flow rate with a simple structure by storing an operating device into a partition in which non- compressive liquid is filled, and discharging/intaking liquid by changing the capacity of a pump chamber as well as applying positive pressure and negative pressure on the non-compressive liquid.

A gasification system is provided with a pump assembly having an inlet connected to a sump and a gasification device assembly. Each pump P of the pump assembly is provided with a pump chamber 60 in which liquid flows from an inlet 52 when valves 56, 58 are opened, and the pump chamber 60 is provided with a partition 62 which is separated by a bellow seal 64 which is capable of expanding. Oil. is filled into the partition 62 as non-compressive liquid, and ram shaft 66 is inserted into the partition 62 freely to project and retract, and a bellow seal 64 is expanded and contracted through oil when the ram shaft 66 is moved inward or outward at uniform speed. Liquid is sucked into the pump chamber 60 when the bellow seal 64 is contracted, and the liquid is discharged to a gasification device at the time of expansion.