To perform maintenance of a first pump or a first flow passage without stopping a power generation unit.

A cooling system 50 includes: a main cooling seawater pump 11 for pressure-feeding seawater W₁₁; a fire-extinguishing and miscellaneous-use pump 15 for pressure-feeding seawater W₁₂; a pipe 51 for making the seawater W11 pressure-fed by the main cooling seawater pump 11 flow to a power generation unit 20; a pipe 16 for making the seawater W₁₂ pressure-fed by the fire-extinguishing and miscellaneous-use pump 15 flow; and a connection unit 52 that is detachably connected to the pipe 16 and makes the seawater W₁₂ flow to the power generation unit 20. The pipe 51 has a flow-in portion 51a, which is connected to the power generation unit 20 and makes the seawater W₁₁ flow to the power generation unit 20, at an end portion of a downstream side thereof. The connection unit 52 is replaced by the flow-in portion 51a and detachably connected to the power generation unit 20.