A fuel cell system (100) includes: a reforming section (33) generating fuel from water for reforming and a raw reforming material; a raw reforming material feeding section (11a5) feeding the raw reforming material to the reforming section; a fuel cell (34) generating electricity using the fuel and an oxidant gas; a combusting section (36) combusting a combustible component from a fuel electrode of the fuel cell using the oxidant gas; an ignition device (36a2) causing the combustible component fed to the combusting section to be ignited; an oxygen proportion adjusting section adjusting an oxygen proportion of the gas introduced into the combusting section when the combustible component is ignited, to become a correction oxygen proportion allowing the combustible component to be ignited and combusted; and an oxygen proportion changing section changing the oxygen proportion from the correction oxygen proportion to a normal oxygen proportion when a defined condition is satisfied.