In a reforming method for a high temperature type fuel cell in which dimethyl ether is used as fuel gas, and a gas containing hydrogen and carbon monoxide produced by reacting dimethyl ether with carbon dioxide is fed into the anode, the carbon deposition at the time of reforming is prevented. The feeding amounts of dimethyl ether and carbon dioxide from a pipe h1 into the reforming reactor are regulated in such a way that the relation between temperature inside the reforming reactor and the molar ratio of carbon dioxide to dimethyl ether in the reforming reactor falls within the region C.