NOVELTY - A fuel cell system comprises fuel cell, fuel gas supply mechanism, supply amount adjustment mechanism, fuel gas flow passage, purge valve, and control mechanisms. The fuel cell generates power by electrochemical reaction of fuel gas and oxidizer gas. The fuel gas supply mechanism supplies the fuel gas to the fuel cell. The supply amount adjustment mechanism adjusts a supply amount of fuel gas. The fuel gas flow passage passes fuel gas.    USE - For generating power by electrochemical reaction of fuel gas and oxidizer gas.    ADVANTAGE - The invention can suppress an amount of fuel gas discharged even when stop request is output during open circuit voltage check. It suppresses the amount of hydrogen gas discharged at stop of fuel cell.    DETAILED DESCRIPTION - A fuel cell system (1) comprises fuel cell (13), fuel gas supply mechanism (11), supply amount adjustment mechanism (15), fuel gas flow passage (21), purge valve (16), and control mechanisms (17). The fuel cell generates power by electrochemical reaction of fuel gas and oxidizer gas. The fuel gas supply mechanism supplies the fuel gas to the fuel cell. The supply amount adjustment mechanism adjusts a supply amount of fuel gas. The fuel gas flow passage passes fuel gas. The purge valve purges gas in fuel gas flow passage outside. The control mechanism opens the purge valve when stop request of fuel cell system is output. When an activation request is output, the control mechanism controls the supply amount adjustment mechanism so that pressure in the fuel gas flow passage becomes smaller than minimum pressure in normal power generation and larger than atmospheric pressure for period from receiving activation request till determining fuel cell becomes state of being able to normally generate power. An INDEPENDENT CLAIM is also included for fuel cell system activation method comprising supplying fuel gas to fuel cell when activation request of fuel cell is output, adjusting pressure within fuel gas flow passage so that the pressure within the fuel gas flow passage, where the fuel gas passes becomes a value, and purging gas within the fuel gas flow passage outside by pressure adjusted in the second step. The value in the second step is set to become smaller than minimum pressure in normal power generation and larger than atmospheric pressure.    DESCRIPTION OF DRAWING(S) - The figure shows a configuration of fuel cell system.    Fuel cell system (1)    Fuel gas supply mechanism (11)    Fuel cell (13)    Supply amount adjustment mechanism (15)    Purge valve (16)    Control mechanisms (17)    Fuel gas flow passage (21)