A power generation system includes a hydrothermal fluid well including a drilled hole reaching down to a hydrothermal fluid reservoir present below an ocean floor from an ocean floor surface and a casing installed in the drilled hole through a guide base on the ocean floor surface, an anode provided on a flow channel for hot water formed by the hydrothermal fluid well, a cathode provided in seawater other than the flow channel for hot water formed by the hydrothermal fluid well, and an ocean floor device that is connected with the anode and the cathode respectively and extracts generated power so as to operate. Power is easily and stably supplied on the ocean floor.