An image forming method applying X-ray exposure to a photothermographic material having, on at least one surface of a support, an image forming layer containing at least a photosensitive silver halide, a non-photosensitive organic silver salt, a reducing agent for silver ions, and a binder, wherein the photothermographic material is brought into close contact with a fluorescence intensifying screen containing a fluorescent material that emits light, 50% or more of which has a wavelength in a range of 350 nm or more and 420 nm or less.