PURPOSE: To enable a development with a high photosensitivity from an aqueous alkaline developer by using a photosensitive layer contg. a specific photosensitive polyester resin.

CONSTITUTION: The photosensitive layer comprises the photosensitive polyester resin or the modified polyester resin having a photosensitive unsatd. double bond adjacent to an arom. ring as a main molecular chain, and a photosensitive unsatd. double bond and a carboxyl group as a pendant group. The polyester resin is constituted of ≥0.4mol photosensitive unsatd. double bond and the carboxyl group having ≥15 acid value per 1,000g polyester resin. The photosensitive unsatd. double bond adjacent to the arom. ring is derived from a dicarboxylic acid shown by the formula I (wherein R1 is a hydrogen atom, a C1W4 alkyl group). The photosensitive unsatd. double bond which is the pendant of the polyester resin is derived from an epoxy resin shown by the formula II (wherein R1 is the same as mentioned above; R3 is a hydrogen atom, methyl, phenyl group). The image forming material has the high photosensitivity and eanble to develop from the aqueous alkaline developer and is suitable for a photosensitive planographic plate and also is useful for a photoresist.