PURPOSE: To smooth an inner surface of a through hole and stabilize solder paste loadings by a method wherein in the production of a metal mask, after through holes are formed in a metal plate the metal plate is electrolytically polished while' being transported in an electrolytically polishing solution flow by conductive transport means.

CONSTITUTION: By shower nozzles 11, purified water is jetted to the both surfaces of a finished metal mask 6 transported by transport rollers 12 to remove a residual electrolyte 9. Next, while the metal mask 6 is transported by the transport rollers 12, the finished metal mask 6 is dried by hot air from air showers 13. Then, the production of the finished metal mask 6 is completed. A metal mask 5 is electrolytically polished by spray nozzles 8 by a doubleside showering method while being transported in the solution flow of the electrolyte 9 by transport rollers 7, 10.