A fuel cell system 1 includes at least one fuel cell stack 100 having a fuel chamber 30 including a fuel electrode (anode) 15b, an air chamber including an oxygen electrode (cathode) 15c and an electrolyte layer 15a interposed between the fuel electrode 15b and the oxygen electrode 15c, pressure regulating means for regulating a supply pressure of fuel gas hydrogen gas) to be supplied to the fuel chamber 30. The pressure regulating means sets up the supply pressure of the fuel gas at a time when the fuel cell stack 100 starts up power generation higher than the supply pressure of the fuel gas during a normal power generation state in which the fuel cell stack 100 is generating electric power.