An economical metallic material for absorption and desorption of hydrogen comprising an alloy having the general formula represented by AB.sub.x, wherein A is Ca or a metallic material which is an alloy including Ca, B is Ni or a metallic material which is an alloy including Ni, and x is in the range of 3.8-6.3, and exhibiting a hydrogen dissociation equilibrium pressure (or plateau pressure, pressure of the plateau region of hydrogen dissociation pressure-hydride composition isotherm) below 1 atm at normal temperatures.The material of the invention very easily absorbs large amounts of hydrogen and efficiently releases it at other predetermined temperatures, pressure and electrochemical conditions, whereby it is able to store hydrogen safely, usefully and economically. It is also suitable for use especially as media for thermal energy storage such as solar energy, waste heat from the electric power generators, and iron foundries, as the alloy of this invention has a plateau pressure below 1 atm at room temperature and of several atmospheres at 35.degree.-100.degree. C.