PURPOSE: To enable to generate electric power efficiently and in a stable manner irrespective of change in the water level of a river, by mounting water turbines and other means on ships.

CONSTITUTION: Water turbines 7, speed-change means 8 and generator 9 are mounted on ships 6, so that they constitute a power generating system 10 as a whole. Here, since the position of the water turbines 7 is always kept constant with respect to the water surface, the water turbines 7 can be turned always at a high efficiency irrespective of change in the water level of a river.