A fuel cell system to be installed on a vehicle includes a fuel cell, a secondary battery, an SOC detector that detects a temperature and a state of charge of the secondary battery, an accelerator position detector that detects an accelerator depressed amount, and a controller that controls power to be generated by the fuel cell. The controller includes: a required generation power calculator that calculates required generation power based on the accelerator depressed amount and the temperature and the state of charge of the secondary battery; and a maximum required power calculator that calculates maximum required power based on the accelerator depressed amount and the temperature and the state of charge of the secondary battery. The maximum required power includes allowable charging power correlated with a maximum value of charging power. If determining that a condition for rapid reduction in consumption power of a motor is satisfied, the controller sets the allowable charging power to zero and calculates the maximum required power. If the required generation power exceeds the maximum required power, the controller makes the fuel cell generate power responsive to the maximum required power.