An anode gas non-recirculation type fuel cell system includes a fuel cell stack constituted by stacking a plurality of fuel cells, a buffer tank for discharging, to an outside, impurity gas included in anode off-gas exhausted from the fuel cell stack, an impurity gas concentration detector for detecting concentration of impurity gas in the buffer tank, and an anode gas supply unit for supplying anode gas to the fuel cell stack. When pressure-supplying impurity gas in the fuel cell stack to the buffer tank while pulsating a supply pressure by the anode gas supply unit, an activation control is executed by changing, by the anode gas supply unit, at least one of a pulsative pressure and a pulsative cycle of anode gas supply according to concentration of impurity gas in the buffer detected by the impurity gas concentration detector. According to the fuel cell system, it is possible to get adequate concentration of hydrogen gas in a fuel cell stack and to remove impurity at its activation.