A hydrogen generation apparatus comprising: a hydrogen generator configured to generate a hydrogen-containing fuel gas from a raw material gas; a combustor configured to heat the hydrogen generator; a combustion gas supply device configured to supply a combustion gas to the combustor; an air supply device configured to supply air to the combustor; a CO sensor configured to detect carbon monoxide contained in a flue gas discharged from the combustor; and a controller, characterized in that in a case where a temperature of the hydrogen generator is lower than or equal to a first temperature set in advance, the first temperature being lower than temperatures at which carbon deposition onto a catalyst in the hydrogen generator occurs when the raw material gas is alone is fed to the catalyst, or in a case where a first period set in advance has elapsed after combustion by the combustor has ended, the first period being a time from when an operation of combusting the combustion gas in the combustor has ended to when the temperature of the hydrogen generator has become lower than or equal to the first temperature, the controller is configured to: cause the combustion gas supply device to supply the raw material gas as the combustion gas to the combustor; and control an air-fuel ratio to be out of a predetermined range, the air-fuel ratio being a ratio between the air and the combustion gas that are supplied to the combustor, and in a case where the CO sensor does not detect a predetermined carbon monoxide concentration, the controller is configured to: determine that the CO sensor is in an abnormal state; give a notification that the CO sensor is in an abnormal state; or perform control to stop the hydrogen generation apparatus from operating, wherein the controller is configured to cause the hydrogen generator to be cooled down such that the temperature of the hydrogen generator becomes lower than or equal to the first temperature in a case where the temperature of the hydrogen generator is higher than the first temperature and a start-up signal to start up the hydrogen generation apparatus has been inputted. a hydrogen generator configured to generate a hydrogen-containing fuel gas from a raw material gas; a combustor configured to heat the hydrogen generator; a combustion gas supply device configured to supply a combustion gas to the combustor; an air supply device configured to supply air to the combustor; a CO sensor configured to detect carbon monoxide contained in a flue gas discharged from the combustor; and a controller, characterized in that in a case where a temperature of the hydrogen generator is lower than or equal to a first temperature set in advance, the first temperature being lower than temperatures at which carbon deposition onto a catalyst in the hydrogen generator occurs when the raw material gas is alone is fed to the catalyst, or in a case where a first period set in advance has elapsed after combustion by the combustor has ended, the first period being a time from when an operation of combusting the combustion gas in the combustor has ended to when the temperature of the hydrogen generator has become lower than or equal to the first temperature, the controller is configured to: cause the combustion gas supply device to supply the raw material gas as the combustion gas to the combustor; and control an air-fuel ratio to be out of a predetermined range, the air-fuel ratio being a ratio between the air and the combustion gas that are supplied to the combustor, and cause the combustion gas supply device to supply the raw material gas as the combustion gas to the combustor; and control an air-fuel ratio to be out of a predetermined range, the air-fuel ratio being a ratio between the air and the combustion gas that are supplied to the combustor, and in a case where the CO sensor does not detect a predetermined carbon monoxide concentration, the controller is configured to: determine that the CO sensor is in an abnormal state; give a notification that the CO sensor is in an abnormal state; or perform control to stop the hydrogen generation apparatus from operating, determine that the CO sensor is in an abnormal state; give a notification that the CO sensor is in an abnormal state; or perform control to stop the hydrogen generation apparatus from operating, wherein the controller is configured to cause the hydrogen generator to be cooled down such that the temperature of the hydrogen generator becomes lower than or equal to the first temperature in a case where the temperature of the hydrogen generator is higher than the first temperature and a start-up signal to start up the hydrogen generation apparatus has been inputted.