Fuel cell system

A fuel cell system includes a drain valve for a gas-liquid separator in a fuel off-gas flow path to discharge liquid water in the gas-liquid separator, a pressure sensor disposed at a fuel gas supply flow path or the fuel off-gas flow path to detect a gas pressure in the flow path, a power generation state acquisition unit to acquire a power generation state of a fuel cell stack, and a control device. The control device controls the opening and closing of the drain valve based on the power generation state and the gas pressure.