A water-based coating formulation for an electrode plate of an electricity storage device, said water-based coating formulation being adapted to form a coating film layer on the electrode plate, contains at least one resin binder having a saponification degree of 40% or higher and selected from unmodified and modified polyvinyl alcohols and unmodified and modified ethylene-vinyl alcohol copolymers, an electrically conductive material, and a specific polybasic acid or its acid anhydride in a water-based medium containing water as a polar solvent. Per parts by mass of the electrically conductive material (2), the resin binder is from 0.1 to 3 parts by mass and the polybasic acid or the like is from 0.01 to 6 parts by mass. The coating formulation has a solids content from 0.02 mass % to 40 mass %.