PURPOSE: To increase cooling efficiency during formation and dispense with work of adjusting electrolyte specific gravity.

CONSTITUTION: A battery jar forming jig 2 having electrolyte injection paths IP1-IP6 for injecting electrolyte into cells C1=C6 and electrolyte suction paths SP1-SP6 for drawing out electrolyte from cells C1-C6 is attached to the opening of a battery jar body 1. Thus, the electrolyte injection paths IP1-IP6 and the electrolyte suction paths SP1-SP6 are so disposed that electrolyte drawn out from a cell is injected into an adjoining cell, thereby flowing electrolyte in turns through plural cells. At first, electrolyte is circulated between a formation electrolyte storage tank T1 and each cell of the battery jar body 1. Then, in the latter half of formation, electrolyte is circulated between a specific gravity adjusting electrolyte storage tank and each cell of the battery jar body 1.