PURPOSE: To perform pumping efficiently, by installing a piston, provided with a heater, in the pump body connected to the lower end of a lifting pipe, and making the piston go down with the high pressure produced by the heater.

CONSTITUTION: A piston 2 provided with a heater is exposed of the upper half to a pressure chamber 3, and when steam in this pressure chamber 3 is heated by the heater and comes to high pressure, the piston 2 comes down, whereby water being filled up in a pump body 1 is pumped up from a lifting pipe 10. When the piston 2 becomes situated in the specified position inside the pump body 1, a solenoid slector valve 6 is operated, and the high pressure in the pressure chamber 3 is expanded in a storage tank 5 and comes to low pressure. Therefore, water in a low level is pumpable to an elevated spot with strong pumping force.