PURPOSE: To allow a hydrogen nuclear fusion reaction at a low temp. with the simple device by using an alloy contg. one of rare earth elements, Mg, Ni, Co, etc., as a cathode material which impresses voltage between a pair of electrodes immersed in heavy water.

CONSTITUTION: The heavy water and a small amt. of metal salt 2 are filled in a vessel 1 and an anode 3 and cathode 4 consisting of gold are immersed at an adequate spaced interval therein. The voltage is impressed between the anode 3 and the cathode 4 from a constant voltage power source 5. Hydrogen appears on the surface of the cathode 4 and the deuterium ions having positive electricity are absorbed in the electrodes in an initial period if, for example, LaNi5 is first used for the cathode 4 of this constitution and, 20V is impressed between the anode 3 and the cathode 4. Neutrons, gamma rays and exothermic phenomenon are then observed. Any metals which can form a metal hydride are usable as the cathode 4 material. Alloys having a high hydrogen density when converted to a metal hydride, for example, Mg2Ni, FeTi, etc., are preferable for the above-mentioned material.