Provided is an image forming method including providing a photothermographic material having image forming layers containing at least a photosensitive silver halide, a non-photosensitive organic silver salt, a reducing agent, and a binder on both surfaces of a support, imagewise exposing the photothermographic material with a fluorescent intensifying screen, and thermally developing the photothermographic material in a thermal developing apparatus having a heating section, wherein the heating section has at least two heating means and a difference between a sensitivity when the photothermographic material is developed at 25.degree. C. and relative humidity of 75% and a sensitivity when the photothermographic material is developed at 25.degree. C. and relative humidity of 20% is 0.20 or less.An image forming method similar to that described above in which the photothermographic material has an antistatic layer is also provided.