PURPOSE: To obtain water lifting energy by attaching a weight to a piston which is rising in water by its buoyancy and guiding the water displaced by the sinking of piston to a discharge piping via a valve.

CONSTITUTION: A water supply tank 3 is attached to the outer wall of a cylinder 2 having a piston 1 and a suction pipe 5 which has an opening at its top with same area as that of the bottom of the piston 1, said piston 1 and suction pipe 5 being connected via a flexible corrugated material having multiple number of reinforcing frame, a water discharge pipe 10 and a discharged water storage tank being provided at the upper portion of said suction pipe 5, and a weight 13 being attached to said piston 1.