A fuel cell system includes a reforming unit, a carbon monoxide decreasing unit, a fuel cell, a burner unit, a raw gas supply device, and a heating unit. The heating unit is controlled at a start-up operation of the fuel cell system, so as to adjust an amount of a desorbed raw gas desorbed out of components of the raw gas adsorbed to at least one of a reforming catalyst and a carbon monoxide decreasing catalyst such that a ratio of an amount of combustion air to an amount of a raw gas in the burner unit falls within a predetermined range.