NOVELTY - A reformer (20) comprises a heat source unit (27); a reforming reaction unit (23); and a channel member (30) having integrally formed channels (31, 32) to transport a fuel and a reforming gas. The channel member comprises a first channel to transport the fuel, and a second channel disposed in the center of the first channel to transport the reforming gas. The channel member is coil-shaped to wind around an outer surface of a reactor body (24) of the reforming reaction unit.    USE - In a fuel cell system (claimed) using fuels such as methanol, ethanol, liquid petroleum gas (LPG), liquefied natural gas (LNG) or gasoline.    ADVANTAGE - The channel member functions to transfer the heat generated from the heat source unit and the heat of the reforming gas, to the fuel supplied to the reforming reaction unit. As the channel member has the double-pipeline structure, the reforming gas flows in helical direction along the second channel to be cooled by the fuel flowing through the first channel at a relatively low temperature, so that the reforming gas can be maintained at a temperature range corresponding to a specific operation temperature of a stack including an electricity generator. The thermal energy generated by the heat source unit, is circulated through the hermetically-sealed space from the reforming reaction unit to surround region, so that the thermal energy required for reactions of reforming reaction unit can be rapidly transferred. Hence, the reformer exhibits improved reaction efficiency and thermal efficiency; has a simple and compact-size structure; and can easily control the thermal energy required for entire operation of the reformer to maximize operation efficiency.    DETAILED DESCRIPTION - The reforming reaction unit generates the reforming gas containing hydrogen, from the fuel via a fuel reforming reaction, using the heat generated by the heat source unit. The reformer further comprises a carbon monoxide reducing unit; and a housing with a hermetically-sealed space to contain the heat source unit and the reforming reaction unit. The channel member is alternatively wound around a second reactor body of the carbon monoxide reducing unit.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic perspective view of a construction of a reformer.    reformer (20)    reforming reaction unit (23)    reactor body of reforming reaction unit (24)    surround region (25a)    heat source unit (27)    burner body (28)    channel member (30)    integral channels (31, 32)    channel inlets (31a, 32a)    channel outlets. (31b, 32b)