A fuel cell reformer includes a main body having a first pipe with a second pipe inside the first pipe, a thermal source unit in the second pipe, a reforming reaction unit in a first region between the first pipe and the second pipe to generate a reforming gas containing hydrogen through a reforming reaction of a fuel, and a carbon monoxide reduction unit in a region other than the first region between the first pipe and the second pipe to reduce a concentration of carbon monoxide contained in the reforming gas. A thermal treatment unit in the main body supplies thermal energy to the reforming reaction unit and the carbon monoxide reduction unit at a time of initial driving of the reformer such that the supplied thermal energy corresponds to a unique operational temperature range in the reforming reaction unit, and to a unique operational temperature range in the carbon monoxide reduction unit.