PURPOSE: To eliminate requirement for activation under high pressure and to perform activation effectively by feeding a vessel contg. hydrogen storing alloy powder in an electric heating furnace having a specified structure, repeating activation, then, discharging the alloy powder by dipping in inactive fluid.

CONSTITUTION: A vessel 11 filled with hydrogen storing alloy is charged to an electric heating furnace 1 and the alloy powder is heated by a heater 2 while evacuating through a gas drawing pipe 9. Then, gaseous H2 is forced through a H2 feed pipe 8 into the furnace 1 for cooling the furnace. The procedure is repeated plural times. After the procedure, an inactive fluid (e.g. pure water, etc.) being no reactive with the alloy powder is introduced into the vessel 11 through a feed pipe 10, then the alloy powder is dipped in the inactive fluid and discharged in the state shielded from atmospheric air. Since the alloy powder is activated before it is filled in the practical reaction vessel such as heat pump and requirement for activation at higher pressure than the used pressure is eliminated, the practical reaction vessel can be made light weight, and the reaction velocity for absorption and desorption of H2 are prompted. Thus, the reaction efficiency of the practical reaction vessel is improved.