NOVELTY - A nickel-hydrogen secondary battery (2) consists of a container (10) and an electrode group (22) accommodated in an airtight condition with an alkali electrolyte solution in the container. The electrode group consists of a positive electrode (24) and a negative electrode (26) overlaid through a separator (28). The alkali electrolyte solution contains sodium hydroxide as main component of solute. The negative electrode contains a hydrogen storage alloy containing magnesium, nickel, and e.g. scandium, yttrium, lanthanum, cerium, tin, indium, copper, aluminum and/or boron.    USE - Nickel-hydrogen secondary battery is used for portable equipment and hybrid electric vehicles.    ADVANTAGE - The nickel-hydrogen secondary battery has suppressed reduction in operating voltage and suppressed self discharge, maintains high capacity residual ratio even when left for long period of time, is user-friendly, and enables driving of apparatus without malfunction.    DETAILED DESCRIPTION - A nickel-hydrogen secondary battery consists of a container and an electrode group accommodated in an airtight condition with an alkali electrolyte solution in the container. The electrode group consists of a positive electrode and a negative electrode overlaid through a separator. The alkali electrolyte solution contains sodium hydroxide as main component of solute. The negative electrode contains a hydrogen storage alloy having a composition of formula: Ln1-xMgxNiy-zMz, where Ln is scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium and/or zirconium, M is vanadium, niobium, tantalum, chromium, molybdenum, iron, gallium, zinc, tin, indium, copper, aluminum, silicon, phosphorus and/or boron, preferably aluminum, x is 0-0.05, y is 3.3-3.6, and z is 0-0.5. The ratio of lanthanum in Ln is 25% or less.    DESCRIPTION OF DRAWING(S) - The drawing shows a perspective view of the partially fractured nickel-hydrogen secondary battery.    Nickel-hydrogen secondary battery (2)    Container (10)    Electrode group (22)    Positive electrode (24)    Negative electrode (26)    Separator (28)