To provide a solid high-polymer type fuel cell power generator and its operation method wherein a reformed gas of a stable composition to be supplied by generation of a stable steam is enabled without pulsations and wherein shortening of a start-up time of the device is aimed at.

This device is comprised that a steam generating part 11 is installed in a combustion furnace at a reformer 3 and that a steam for reforming is assumed to be generated by feeding a supply-water through the steam generating part 11. In the constitution, for example, the steam generated in the steam generating part 11 is assumed to be a wet steam, this wet steam is assumed to be superheated vapor by spreading it into a cooling tube 9 of a monoxide eliminator 5, further by making this vapor flow into a flow tube 7a of the vapor cooling a catalyst for carbon monoxide conversion installed at the circumferential part of the reformer, and this superheated vapor is made to flow into the reforming catalyst part of the reformer 3 together with a raw material fuel gas.