PURPOSE: To reduce the self discharge of a lead acid battery by making a casting mold for cast on strap from a stainless material mainly composed of iron.

CONSTITUTION: A casting mold 1 for cast on strap, consisting of stainless steel material SUS304 mainly composed of iron, has a flat plate-shaped main unit 2 and a handle 3 extended upward from one side of this main unit 2, to form a recessed part 2a opened with an upper surface corresponding to a negative pole strap 10 and a recessed part 2b opened with an upper surface corresponding to a positive pole strap 11, in the main unit 2. The recessed parts 2a, 2b, providing a gradient in a side surface, are spread in accordance with going upward, and the straps 10, 11, when formed, are easily drawn out from the recessed parts 2a, 2b. The handle 3 of the casting mold 1 is gripped to immerse the casting mold main unit 2 in a molten metal 5 of a dissolution bath 11. The main unit 2 is horizontally placed, taken out from the dissolution bath 4 and cooled by a cooling device, and the straps 10, 11 are separated from the recessed parts 2a, 2b of the casting mold 1, to complete a electrode plate group.