A reforming device includes a reforming portion generating reformed gas from a mixed gas, in which fuel and steam are mixed and including a reforming portion loop-back channel provided at the reforming portion so as to extend along an axis line thereof, a combusting portion provided at an inner circumference of the reforming portion in order to generate combustion gas, a combustion gas channel including a loop-back channel within which the combustion gas flows, an evaporating portion generating steam by heating water and supply steam to the reforming portion; and a carbon monoxide reducing portion provided at an outer circumferential wall of the evaporating portion in order to reduce a level of carbon monoxide in the reformed gas that has been exhaled by the reforming portion, and in order to supply such reformed gas to a fuel cell.