PURPOSE: To improve image forming efficiency with the quick formation of a dye film on the back of a gas permeable film by providing a nozzle for injection of dye to the gas permeable film and a member for supply of dye under pressure to the nozzle.

CONSTITUTION: For image formation, a sublimating or evaporating dye 14 is charged into a container and a blower 4 is operated. The dye 14 is injected from a nozzle 6 to be stuck to the back of a gas permeable film 8. Thus a film 14' is formed and residual dye 14 is returned to the blower 4 through a return channel 3. Later a thermal head 9 is heated in accordance with an image signal to be transmitted to the former, gasifying the part of the film 14' corresponding to the thermal head. This enables the dye to penetrate through the gas permeable film 8 and an image to be formed on a receptor paper 12. In the meantime, the thermal head 9 moves with the container 1, forming a single line of image on the receptor paper 12 over a platen roller 13. If this process is terminated, the platen roll rotates to move the receptor paper by a single line, while the thermal head returns to its original position. This process is repeated, ending formation of a required image.