NOVELTY - The hydrogen generator has sealed container(s) (6) having water-storing portion (18) and hydrogen reservoir chamber, and powder supply device (7) attached to container. The powder supply device supplies magnesium alloy powder (p) to portion (18). The generator is used for reacting aggregate of magnesium (Mg) alloy particle and catalyst metal microparticles, and water (19) to produce hydrogen.    USE - For hydrogen generation in fuel cells.    ADVANTAGE - The hydrogen generator is inexpensive and simple. The waste-liquid processing is performed easily. The hydrogen is generated rapidly with high production rate.    DETAILED DESCRIPTION - The hydrogen generator has sealed container(s) having water-storing portion in its lower portion with water surface space (20) and hydrogen reservoir chamber (21) in its upper portion, and a powder supply device attached to the sealed container. The powder supply device supplies magnesium alloy powder to portion (18). The hydrogen generator is used for reacting aggregate of magnesium alloy particle and water to produce hydrogen. The aggregate of magnesium alloy grain consists of grain shape magnesium inside the alloy and catalyst metal microparticles at the surface. The catalyst metal microparticles are chosen from at least one type of nickel and its alloy microparticles, iron and/or its alloy microparticles, vanadium and/or its alloy microparticles, manganese and/or its alloy microparticles, titanium and/or its alloy microparticles, copper and/or its alloy microparticles, gold and/or its alloy microparticles, calcium and/or its alloy microparticles, zinc and/or its alloy microparticles, zirconium and/or its alloy microparticles, cobalt and/or its alloy microparticles, chromium and/or its alloy microparticles, and aluminum and/or its alloy microparticles.    DESCRIPTION OF DRAWING(S) - The figure shows sectional drawing of the hydrogen generator.    sealed container (6)    powder supply device (7)    water-storing portion (18)    water (19)    hydrogen reservoir chamber (21)    magnesium alloy powder (p)