High pressure superheated steam above the critical temperature (374 degrees C) and below the critical pressure (22.1MPa) of water was used to produce hydrogen gas from waste biomass efficiently. The targets are large amount of waste biomass such as livestock excrement and paper sludge. We investigated the effects of reaction temperature, pressure, time, catalyst and molar ratio of water to carbon in biomass on the decomposition efficiency of waste biomass and the productivity of hydrogen. Almost 100% of the decomposition efficiency and 1350-1550cm(3) of hydrogen production per gram of dry biomass were realized in the presence of KOH catalyst at 700 degrees C, 10MPa, 20min and 20 of molar ratio of water to carbon in biomass.