A fuel cell system includes: a fuel cell in which a plurality of cells are stacked; a voltage sensor configured to measure a cell voltage of the fuel cell; and a pressure sensor configured to measure an anode gas pressure in the fuel cell. When the cell voltage is lower than a predetermined threshold voltage, in a state in which an amount of supply of cathode gas to the fuel cell is secured, and a rate of decrease in the anode gas pressure is larger than a predetermined threshold rate, it is determined that a cross leak abnormality has occurred in the fuel cell.