Processing composition for printing plate

A processing composition which is used for lithographic printing plate where silver image is used as ink receptive area and which contains an organic compound having two or more mercapto groups or thione groups wherein said composition additionally contains an aromatic sulfonic acid formalin condensate which is represented by the following formula, ##STR38## wherein n is an integer or 1 ore more and M represents an alkali metal atom, an anionic surfactant having a polyoxyethylene group, which is represented by the following formula:

• ##STR39## wherein R represents a substituted or unsubstituted alkyl, alkenyl or aryl group of 1-30 carbon atoms, Q represents ##STR40## wherein R1 represents a hydrogen atom or a substituted or unsubstituted alkyl group;
• B represents a divalent group;
• m is O or an integer of 1 ore more;
• A represents --SO.sub.3 M, --COOM, --O--SO.sub.3 M, ##STR41## wherein M represents a cation, and B, Q and R are as defined above;
• and n which is an average polymerization degree of methylene oxide is 1-50, an aromatic carboxylic acid, which is represented by the following formula:
• ##STR42## wherein X represents a hydrogen atom, an alkali metal atom, an ammonium ion, an alkyl group or an aryl group, Y represents a halogen atom, an alkyl group, an alkoxy group, an amino group, a hydroxy group, a nitro group, a sulfonic acid group, or a carboxylic acid group, Z represents a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group, amino group, a nitro group, a sulfonic acid group, or a carboxylic acid group and n is 0, 1, 2, or 3 and when n is 2 or 3, Y may be identical or different, a hydrosulfite compound, which is represented by the following formula:
• ##STR43## wherein A represents a hydroxyl group, an amino group or ##STR44## with the carbon atom to which they bond or one of R1 and R2 represents a hydrogen atom and the other represents a hydrogen atom, an alkyl group, an aryl group or a hydroxyl group, n is 0 or an integer of 1-8, Q represents --SO.sub.3 M or --SO.sub.2 M and M represents a cation, a hydroxyaryl fatty acid, which is represented by the following formula:
• ##STR45## wherein R.sub.1 represents a straight chain alkyl group of 1-19 carbon atoms or a hydrogen atom, R.sub.2 represents a straight chain alkylene group of 1-19 carbon atoms, sum of carbon numbers of R.sub.1 and R.sub.2 is 10-20, and R.sub.3 and R.sub.4 each represents a hydrogen atom, a hydroxyl group, or an alkyl or alkoxy group or 1-9 carbon atoms, or an organic disulfide compound, and wherein said composition additionally contains an oxidizing agent.