A plate-fin-type methanol reformer was made by preparing Cu-Zn/Al2O3/Al-plate and Pt/Al2O3/Al-plate catalysts on an aluminum plate with aluminum fins on the surfaces of both sides. Feed gas composed of methanol and steam was supplied to the Cu-Zn/Al2O3/Al-plate-catalyst side and combustion gas composed of hydrogen and air was supplied to the Pt/Al2O3/Al-plate-catalyst side. The methanol steam-reforming reaction, which is endothermic, was carried out on the Cu-Zn/Al2O3/Al-plate catalyst and the hydrogen-oxygen combustion reaction, which is exothermic, was carried out on the Pt/Al2O3/Al-plate catalyst to supply the heat needed for the methanol steam-reforming reaction to the other side. This reformer's steam-reforming characteristics are superior to those of a fixed-bed-type methanol reformer with commercial CuO-ZnO-particle and Pt/Al2O3-particle catalysts. The gas temperature of its catalytic combustion part was similar to that of the methanol steam-reforming part at each point in the gas-flow direction. In the fixed-bed-type methanol reformer, on the other hand, it was about twenty degrees higher. The start-up time of the plate-fin-type methanol reformer was 28% of that of the fixed-bed-type methanol reformer. And its overall heat transfer coefficient was 16 times larger. Therefore, we conclude that this large overall heat transfer coefficient contributes to its higher performance and shorter start-up time as well as its large apparent heat transfer surface area. The catalyst volume in the plate-fin-type methanol reformer was only 11% of that in the fixed-bed-type one even though its methanol steam-reforming characteristics were superior. Thus, the plate-fin-type methanol reformer is an effective way to reduce the reformer size and start-up time.