Since the hydrolysis of the hydrogen generating material in pure water is very slow (see curve "H2O" in Figure (a) as an example for MgH2), there is no significant hydrogen release at this stage. Then the orifice of the reactor is closed with a dosing plug (2) equipped with pipelines for acid supply (2a) and hydrogen outlet (2b); the opposite ends of the pipelines are connected to the acid supply and gas distributing systems, respectively. The former comprises of the reservoir (3) filled with the acid solution (3a) supplied via valve (4). The gas distributing system includes pipeline (5) which connects gas outlet of the reactor (1) with the opposite (upper) end of the sealed reservoir (3) thus maintaining the equal pressures in the gas spaces of reactor (1) and reservoir (3). Additionally, it includes gas manifolds (6), overpressure safety valves (7), pressure sensor (8) and hydrogen purifier (9) which removes mist and water vapour from hydrogen released in reactor (1) when the acid solution is supplied thereto via valve (4).