We studied the hydrogen production from four kinds of wet food wastes using high pressure superheated steam, which is reactive water above the critical temperature and below the critical pressure of water. 1.8-2.0 mmoles of hydrogen gas were produced from 1 mmole of organic carbon in the wastes at 700 degrees C, 10 MPa, 30 min, 20 of the molar ratio of water to organic carbon and 20 wt% of the potassium hydroxide to the organic content in the waste. The production of hydrogen gas was accelerated by increasing the temperature and molar ratio of water to organic carbon in the waste, but suppressed by increasing the pressure. On the other hand, the production of ammonia, which is a typical by-product of gasification of food wastes, reduced by increasing the temperature and decreasing the pressure. Judging from the experimental results, high pressure superheated steam with low pressure was more effective than supercritical water with high pressure. The calculated equilibrium mole fractions of hydrogen gas based on the ideal gas assumption agreed with the experimental data in wide temperature and pressure regions, but those of methane and carbon dioxide deviated from the data above 600 degrees C.