To provide a power generation system that pumps up ground water stored in a pumping well without electric power to pour it to an injection well, thereby generating electric power without impairing the efficiency of power generation.

A pumping port at one end of a siphon tube is inserted into the ground water in the pumping well which is fluidly connected to an upper aquifer, and an injection port at the other end is inserted into a position below a water level of the pumping well in the injection well which is fluidly connected to a lower aquifer and in which a water level of the ground water is lower than the pumping well. The ground water continuously flowing in the siphon tube from the pumping well by the action of the siphon rotates a turbine to generate electric power.