A fuel cell system comprising: a reforming section that generates fuel from water for reforming and a raw reforming material; a reforming-section temperature detecting section that detects a temperature of the reforming section; a raw reforming material feeding section (11a5) that feeds the raw reforming material to the reforming section; a fuel cell that generates electricity using the fuel and an oxidant gas; a combusting section that combusts a combustible component discharged from a fuel electrode of the fuel cell using the oxidant gas; an ignition device (36a2) that causes the combustible component fed to the combusting section to be ignited; an oxygen proportion adjusting section that adjusts an oxygen proportion (λ) of the gas which is introduced into the combusting section when the combustible component is ignited in the ignition device (36a2), to become a correction oxygen proportion (λ1, λ2) which allows the combustible component to be ignited and combusted; and an oxygen proportion changing section that changes the oxygen proportion (λ) from the correction oxygen proportion (λ1, λ2) to a normal oxygen proportion (λ2-2) when a defined condition is satisfied, characterized by a combustion section temperature sensor that detects a temperature of the combusting section; and an ignition and combustion determining section that determines whether or not ignition or combustion occurs in the combusting section, wherein the oxygen proportion adjusting section lowers the correction oxygen proportion (λ1, λ2) every time the ignition and combustion determining section determines that ignition does not occur or that blow-off occurs in the combusting section, wherein after ignition in the combusting section succeeds and if a starting condition is established, the oxygen proportion changing section changes the oxygen proportion (λ) to the start correction oxygen proportion (λ2), the starting condition being a case where a temperature detected by the combustion section temperature sensor is equal to or higher than a start temperature, or a case where a change amount of the combustion section temperature sensor per unit time is equal to or greater than a start change amount, and wherein the oxygen proportion changing section changes the oxygen proportion (λ) from the start correction oxygen proportion (λ2) to the normal oxygen proportion (λ2-2) larger than the start correction oxygen proportion (λ2) when the temperature detected by the reforming-section temperature detecting section is equal to or greater than a defined temperature. a reforming section that generates fuel from water for reforming and a raw reforming material; a reforming-section temperature detecting section that detects a temperature of the reforming section; a raw reforming material feeding section (11a5) that feeds the raw reforming material to the reforming section; a fuel cell that generates electricity using the fuel and an oxidant gas; a combusting section that combusts a combustible component discharged from a fuel electrode of the fuel cell using the oxidant gas; an ignition device (36a2) that causes the combustible component fed to the combusting section to be ignited; an oxygen proportion adjusting section that adjusts an oxygen proportion (λ) of the gas which is introduced into the combusting section when the combustible component is ignited in the ignition device (36a2), to become a correction oxygen proportion (λ1, λ2) which allows the combustible component to be ignited and combusted; and an oxygen proportion changing section that changes the oxygen proportion (λ) from the correction oxygen proportion (λ1, λ2) to a normal oxygen proportion (λ2-2) when a defined condition is satisfied, characterized by a combustion section temperature sensor that detects a temperature of the combusting section; and an ignition and combustion determining section that determines whether or not ignition or combustion occurs in the combusting section, wherein the oxygen proportion adjusting section lowers the correction oxygen proportion (λ1, λ2) every time the ignition and combustion determining section determines that ignition does not occur or that blow-off occurs in the combusting section, wherein after ignition in the combusting section succeeds and if a starting condition is established, the oxygen proportion changing section changes the oxygen proportion (λ) to the start correction oxygen proportion (λ2), the starting condition being a case where a temperature detected by the combustion section temperature sensor is equal to or higher than a start temperature, or a case where a change amount of the combustion section temperature sensor per unit time is equal to or greater than a start change amount, and wherein the oxygen proportion changing section changes the oxygen proportion (λ) from the start correction oxygen proportion (λ2) to the normal oxygen proportion (λ2-2) larger than the start correction oxygen proportion (λ2) when the temperature detected by the reforming-section temperature detecting section is equal to or greater than a defined temperature.