PURPOSE: To enable the redissolution of a developer concentrate after freezing and the dilution with tap water and to obtain a developer having satisfactory developing characteristics by incorporating an oligomeric phosphate and/or an alkali metallic salt of N(2-hydroxyethyl)ethylenediaminotriacetic acid into the concentrate.

CONSTITUTION: This developer concentrate is made of a mixture of water with an org. solvent, a reagent exhibiting alkaline reaction, an anionic surfactant, n-alkanic acid and/or its salt, an emulsifier, a buffer and a complexing agent. An oligomeric phosphate and/or an alkali metallic salt of N-(2- hydroxyethyl)ethylenediaminotriacetic acid is used as the complexing agent. This concentrate can be redissolved after freezing, can be diluted with tap water and gives a developer having satisfactory developing characteristics. When a substrate of Al, etc., is coated with a negative processable layer contg. a diazonium salt and a binder and the layer is developed with a developer obtd. by diluting this concentrate with water, the objective printing plate is produced.