Hydrogen storage alloy has: (1) a main composition expressed by the formula of Mm-(Ni--Al--Co--Mn--Mo); (2) a ratio of the number of atoms expressed by the formula of (Ni--Al--Co--Mn--Mo) is 5.7<(Ni+Al+Co+Mn+Mo).ltoreq.8, and 3.5.ltoreq.Ni, when Mm is set at 1 in a ratio of the number of atoms; and (3) an internal structure having hydrogen storage alloy phase expressed by the general formula of AB.sub.5, and a second phase existing in the hydrogen storage alloy phase.