To produce a transmitting original for exposure of a photographic printing paper having both of quality of printed characters and durability of an image while utilizing features of a melt-thermal transfer method which is inexpensive and excellent in maintenance property, and to provide an image forming method using the obtd. original.

This image forming method includes the following processes. First an ink sheet having a coloring material layer on one surface and a heat- resistant layer on the opposite surface of a transparent supporting body is laminated with an image accepting sheet on the coloring material layer side. The ink sheet is heated by a heating device through the heat-resistant layer according to the image so as to transfer the color layer in a heated part to the image-accepting sheet. Then the ink sheet with the image formed is laminated. The laminated image is used as a transmitting original to expose a negative silver halide photographic sensitive material. Then the negative silver halide photographic photosensitive material after exposure is developed.