To obtain a positive type image forming material excellent in sensitivity, resistance (development latitude) to a high concentration developer, chemical resistance and microdot reproducibility.

A photosensitive layer containing a dye having its absorption band in infrared light and a novolak resin is disposed on a substrate to obtain the objective image forming material. The area ratios of GP patterns of the novolak resin whose weight average molecular weight (expressed in terms of polystyrene) measured by GPC using monodisperse polystyrene as a standard is in the ranges of 6,000-30,000, 2,000-5,000 and 100-1,000 to the total area are 30-90%, 0-40% and 20-90%, respectively. The image forming material contains a compound capable of generating an acid under light or heat and a compound having at least one bond that can be decomposed by the acid. The image forming material is exposed with laser and developed with an aqueous alkali solution to form the objective image.