To obtain an exposure device for a photosensitive planographic printing plate which does not form the portions of a positive type printing original plate, which portions are held by plate end and plate tail clamping mechanisms, as image parts when the printing original plate is mounted at a plate cylinder.

This exposure device has the plate cylinder 11 mounted with the printing original plate. The plate cylinder 11 is provided with the plate end clamping mechanism 12 for holding the plate end which is the front end of the printing original plate 70 and the plate tail clamping mechanism 13 for holding the plate tail which is the rear end of the printing original plate 70. The respective clamping mechanisms 12 and 13 have lower teeth 12b and 13b and upper teeth 12a and 13a which are respectively turnably supported by the lower teeth and are capable of holding the plate tip or the plate tail between the lower teeth and the front surfaces of the lower teeth. The upper teeth 12a and 13a of the plate end and plate tail clamping mechanisms 12 and 13 consist of resins transparent to IR light.