PURPOSE: To enable massproduction of grids for a lead storage battery to be easily performed by providing a panel-like polyhedral grid constituted of a plural number of unit grids with a reinforcing crosspiece made of an acid-proof synthetic resin when making lead-synthetic resin complex grids by immersing the grids in molted lead.

CONSTITUTION: A grid base 1 consisting of a polypropylene or the like is immersed in molten lead in such a manner as to form a thin lead film 2 only on an area required to be conductive so as to make a lead-synthetic resin complex grid. Here, after six pieces of unit grids 5 are arranged in a line to form each of the upper and the lower sections of a grid structure, a belt-like acid-synthetic- resin reinforcing crosspiece 7 integrated with a supporting section 8 is placed between the above two sections to make a polyhedral grid. After that, the area below the line (a) and the area above the line (a') are immersed in molten lead. By the means mentioned above, the mechanical strength of the polyhedral grid is increased, the sag and the fall of electrode plates are suppressed and massproduction of grids can be easily performed.