NOVELTY - Hydrogen generator comprises reformer (10); water evaporator (9); material flow passage (1); shifter (15); reformed gas flow passage (RGFP) (2); shifted gas flow passage (3) and combustor. Part of heat of gas flowing through RGFP is used to generate steam in evaporator by heat exchange and cools reformed gas and radiation heat from shifter is transferred to evaporator through RGFP to generate steam.    USE - For fuel cell power generation system configured to generate electric power (claimed).    ADVANTAGE - More heat is recovered in heat exchange between water and the reformed gas than in heat exchange between gases e.g. combustion fuel gas, air, or feed gas and the reformed gas. As a result, thermal efficiency is improved. Since temperature control of the shifter is carried out by using water, externally supplied, without being affected by other parts within the generator, controllability is improved. In particular, regardless of load fluctuation in the amount of hydrogen generation in the reformer, high temperature controllability can be achieved. Further, since the radiation heat is used to generate the steam in the evaporator, thermal efficiency is further improved. The construction of evaporator and shifter is such that pool boiling caused by heating from below is realized, and hence, pressure fluctuation caused by bumping can be inhibited. As a result, the amount of hydrogen or carbon monoxide contained in the reformed gas generated in the reformer is stabilized and hence the reforming reaction is carried out stably in the reformer. Since the bumping is inhibited in the hydrogen generator, the metal ions contained in water are inhibited from flying. Thus, durability of the generator is improved. The hydrogen generator may further comprise a temperature detector configured to detect temperature of the shifter and amount of the water supplied is thus adjusted. Thereby, high temperature controllability is achieved, and hence the shifter can be kept at an optimal temperature for a shift reaction.    DETAILED DESCRIPTION - The reformer is configured to reform a material using steam supplied from a water evaporator to generate a reformed gas containing hydrogen as a major component. Through material flow passage steam and the material are supplied to the reformer. The shifter is configured to shift carbon monoxide contained in the reformed gas into carbon dioxide by a shift reaction. Through the reformed gas flow passage the reformed gas is sent to the shifter. The combustor is configured to heat the reformer using a combustion gas.    DESCRIPTION OF DRAWING(S) - The drawing shows a cross-sectional view of the hydrogen generator.    material flow passage (1)    reformed gas flow passage (2)    shifted gas flow passage (3)    water evaporator (9)    reformer (10)    shifter. (15)