Image forming method for the photothermographic material

An image forming method comprising:

• imagewise exposing and thermal developing a sheet-like photothermographic material using an image recording apparatus, wherein a part of the sheet is exposed and, in parallel with the exposure, development is started on a part of the sheet having been already exposed:
• wherein the photothermographic material comprises at least a photosensitive silver halide, a non-photosensitive organic silver salt, a reducing agent represented by following formula (R) and a binder on at least one surface of a support;
• wherein R11 and R11′ each independently represents an alkyl group having 1 to 20 carbon atoms, R 12 and R12′ each independently represents a hydrogen atom or a group capable of substituting for a hydrogen atom on a benzene ring, L represents a —S— group or a —CHR13— group, R13 represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms, and X and X1 each independently represents a hydrogen atom or a group capable of substituting for a hydrogen atom on a benzene ring;
• and
• wherein the photosensitive silver halide contains at least two preformed photosensitive silver halides having respective sensitivities different from each other for a light with the same exposure wavelength and a silver iodide content of the photosensitive silver halide is 40% by mole or more.