NOVELTY - A hydrogen storage alloy contains calcium-copper-type crystal phase as a main phase. The storage alloy contains at least one lanthanoid element including yttrium, and lanthanum as essential component, and element chosen from titanium, zirconium, hafnium, silver, germanium, and vanadium. The hydrogen storage alloy has a structure in which a precipitation phase of 5 mu m or more is not contained in mapping image of tin and lanthanum having magnification of X800, obtained by area analysis performed using EPMA of cross-sectional structure of alloy.    USE - Hydrogen storage alloy is used for negative electrode of nickel hydrogen secondary battery (all claimed) used as power supply for portable apparatus e.g. digital camera, electric vehicle and electric tool.    ADVANTAGE - The hydrogen storage alloy has high corrosion resistance and oxidation resistance, and is economically manufactured. The hydrogen storage alloy provides nickel hydrogen secondary battery with excellent cycle characteristics and self discharge characteristics.    DETAILED DESCRIPTION - A hydrogen storage alloy contains calcium-copper (CaCu5)-type crystal phase as a main phase. The storage alloy has compositional formula: RNiaCobAlcMndSneMf, where R is element including at least one lanthanoid element including yttrium, and lanthanum as essential component, preferably lanthanum (30 %mass or less), cerium (5-55 %mass), praseodymium (0.1-1 %mass) and neodymium (0.1-20 %mass) M is chosen from titanium, zirconium, hafnium, silver, germanium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, iron, copper, zinc, boron, gallium, antimony, indium, silicon, phosphorus and carbon, a is 3.7-5.1, b is more than 0 and 0.55 or less, preferably 0.1-0.3, c is 0-0.45, d is 0 or more and less than 0.2, e is 0.05-0.25, preferably 0.05-0.15, f is 0-0.25, a+b+c+d+e+f is 4.9-5.5, b+e is 0.15-0.45 and d+e is 0.05-0.3. The hydrogen storage alloy has a structure in which a precipitation phase of 5 mu m or more is not contained in mapping image of tin and lanthanum having magnification of X800, obtained by area analysis performed using EPMA of cross-sectional structure of alloy.