To provide a positive lithographic printing original plate for IR laser for direct plate making which has a recording layer excellent in the latitude for image formation by development and excellent in the resistance against scratches.

The original plate is obtained by forming a positive recording layer which contains a water-insoluble and alkali-soluble resin having a siloxane structure and an absorbent for IR rays and which increases its solubility with an alkali aqueous solution by exposure to IR laser beam on a supporting body. The resin soluble with an alkali aqueous solution is prepared by introducing at least one kind of substituent having a siloxane structure (Si-O) into a well- known polymer compound soluble with an alkali aqueous solution.