To provide a liquid pressure feeder preventing noise and vibration when a flush steam of condensed water flowing through a drain pipe is mixed with liquid flowing through a conveying pipe.

An air inlet 6 and an air outlet 7 for working steam and an inlet 8 and an outlet 9 for force feed liquid are provided in the liquid pressure feeder 24. An inflow pipe 21 is connected to the inlet 8, the conveying pipe 25 is connected to the outlet 9, an air supply pipe 26 is connected to the air inlet 6, and an exhaust pipe 23 is connected to the air outlet 7. The drain pipe 27 is branched off from the air supply pipe 26 and connected to the conveying pipe 25. A steam trap 28 and a discharge side check valve 29 allowing only a flow of condensed water to the conveying pipe 25 are arranged on the drain pipe 27. A mixing chamber 30 of the flush steam of the condensed water flowing through the drain pipe 27 and the liquid flowing through the conveying pipe 25 is formed on a connection part of the drain pipe 27 and the conveying pipe 25, and a nozzle part 32 injecting the flush steam into the mixing chamber 30 and a suction opening 34 sucking in the liquid by the flush stem injected from the nozzle part 32 are provided on a trailing end of the drain pipe 27.