An image forming method using a photothermographic material including, on at least one surface of a support, at least a photosensitive silver halide, a non-photosensitive organic silver salt, a reducing agent for silver ions, and a binder, in which (1) the photothermographic material is exposed and thermally developed during transportation at a transportation speed of 23 mm/sec or faster, (2) the non-photosensitive organic silver salt contains 30 mol % to 85 mol % of silver behenate and an amount of the time until a leading end of the photothermographic material reaches a thermal development station after a power source for ae thermal developing apparatus is turned on is 15 minutes or less, or (3) a coating amount of silver inf the photothermographic material is 1.9 g/m.sup.2 or less and a thermal development time is 12 sec or less.