To produce high-pressure hydrogen, water and a hydrogen-generating material (MgH₂) which reacts with water to generate hydrogen are weighed so that a target high hydrogen pressure is generated in a high-pressure container. Then, the hydrogen-generating material is introduced into the high-pressure container through its supply port, and water is introduced into the high-pressure container through the supply port. Thereafter, the supply port is closed, thereby causing a reaction between the hydrogen-generating material and the water, so that the hydrogen pressure in the high-pressure container reaches a target high hydrogen pressure.