To provide an image forming method using a heat developable photosensitive material by which the size of an image part is not changed even when the heat developable photosensitive material is used for printing and the size of the material is changed by heat development, and thereby, without causing any misalignment in colors.

In this image forming method using the heat developable photosensitive material, the heat developable photosensitive material containing an org. silver salt, photosensitive silver halide, reducing agent and hydrazine driv. or quaternary onium salt compd. on a substrate is subjected to scanning exposure in an exposure device which is equipped with an image processing portion to magnify or reduce the digital data of an image and with a scanning exposure portion to scan and expose the material with laser beams, and then subjected to heat development.