A hydrogen supply method for a fuel cell system, for supplying hydrogen according to a state of the fuel cell system when the fuel cell system is started, includes steps of (a) measuring a stop time period which elapses until the fuel cell system is started after the fuel cell system is stopped, (b) determining whether a reaction time period consumed to complete a reaction of residual hydrogen and residual oxygen residing in a fuel cell stack since the fuel system is stopped is not more than the stop time period, and (c) when it is determined in the step (b) that the stop time period is less than the reaction time period, closing a purge valve that is able to discharge gases accommodated in an anode from the anode and supplying at the same time hydrogen to the anode such that an internal pressure of the anode becomes a predetermined first target pressure.