To generate electric energy, by using potential energy generated in a floating body by buoyancy in the sea and rivers.

This ladder type power generator: includes a means for connecting the floating body existing at least on the sea and the rivers and an object of not receiving influence of the buoyancy such as the land; converts a change in relative displacement generated between the buoyancy of the floating body and the object of not receiving the influence of the buoyancy such as the land, into an angular change and a positional change in the connecting means; and converts the change into power generation energy.