To improve the developing rate and image reproducibility even when water with high hardness or low hardness is used, by incorporating a hydrophilic component containing ionic hydrophilic groups.

The developer is used to remove an unexposed part of a photosensitive resin plate after exposure, and the resin plate has a photosensitive resin compsn. layer which contains one of ionic hydrophilic groups expressed by (a) -COOM, (b) -SO3M- (c) -SO4M, and (d) (-O)3-nPO(OM)M. To the developer, a compd. having an ability to form a chelate compd. with polyvalent metal ions and/or phosphoric acids are added. In the formulae, M is a uni- or bivalent metal atom or an ammonium compd. and (n) is 1 or 2. As for the photosensitive resin compsn., it contains a hydrophilic component containing ionic hydrophilic groups in order to have developing property with a water-based developer. Photosensitivity is given to the components above described by adding photopolymerizable unsatd. monomers, photosensitizer and other additives.