An alkaline battery sealing gasket 33 made of a resin, comprises a peripheral packing portion 36 sandwiched in a pressed state between an opening end of a metal battery can 11 that contains an electricity generating element 20 and doubles as a positive electrode terminal and a negative electrode terminal 32 so as to seal the opening end with an airtight manner; and an isolation wall portion 37 for isolating a space on a back side of the negative electrode terminal from a space containing the electricity generating element, wherein in the isolation wall portion, a thinner portion 38 to break open earlier due to increases in gas pressure in the containing space to function as a safety valve is formed groove-like. A groove direction of the thinner portion 38 is in the same direction as an orientation of the resin of the gasket, and an Izod impact value of the resin forming the gasket is in a range of 20 to 60 J/m (at a temperature of 23±2° C. and a relative humidity of 50±5%).