To obtain a plate making method for planographic printing plates which allows the always adequate setting of at least one regulation conditions among the replenishing amount of a removing liquid, temperature of the removing liquid and removing process time when removing an oxygen shielding layer according to the sizes and kinds of the PS plates provided with photopolymerization layers having the over-coating layers on the uppermost layers and eliminates the possibility of operation errors, etc., in the removing process of over-coating layers to be executed before the development processing of the PS plates.

A processor control section 30 of an automatic developing machine 16 online acquires various kinds of set information on the kinds, sizes, etc., of the PS plates inputted to a plate setter 14, determines the removal conditions for the over-coating layers in accordance with various kinds of the acquired set information and regulates the replenishing amount of the washing water, the temperature of the washing water and the process time in such a manner that the determined removal conditions may be attained.