To save the energy of power by constituting the system in such a way that a pressure reducing cylinder having slender, sealed construction and a discharge adjusting tank are placed in parallel, so that the liquid within the pressure reducing cylinder is discharged from a discharge port by means of the natural force once the water is pumped up into the pressure reducing cylinder through the operation of the pressure reducing pump provided on the upper part of the pressure reducing cylinder.

Before the use of a pump, liquid is poured up to the discharge head H-1 of a discharge pipe 9 connected to the bottom of a pressure reducing cylinder 1 and of a discharge adjusting tank 5, while a piston 7 within the adjusting tank 5 is moved down to the bottom, and the inside of the piston 7 is filled with the liquid. After the start of the operation, a water supplying valve B-1 is opened, and a pressure reducing pump (C) is operated so as to reduce the pressure within the pressure reducing cylinder 1. This pressure reducing operation continues until the liquid is discharged from a discharge port (O), and after this, the pumping is conducted continuously through the natural force. When the pumping is to be stopped, the water supplying valve B-1 is closed. When the pumping is to be restarted, water pumping-up can be done only by releasing the water supplying valve B-1.