A fuel gas injection device of a fuel cell system includes an ejector having a nozzle that generates a negative pressure by discharging a fuel gas injected respectively from a plurality of injectors so as to draw-in a fuel exhaust gas discharged from a fuel cell stack and mix the fuel exhaust gas with the fuel gas. A total orifice equivalent diameter obtained by adding together orifice equivalent diameters of respective injection holes of the plurality of injectors and an orifice equivalent diameter of an injection hole of the nozzle are set such that SE