PURPOSE: To simplify constitution and to reduce production cost by using a capsule paper having three-layered structure and a single laser corresponding to the photosensitive characteristic of the capsule paper.

CONSTITUTION: The device is provided with the single lasers 20-22 corresponding to the absorption wavelength of the capsule paper 80 consisting of three layers such as a Y layer, an M layer and a C layer, a condensing lens 35 for converging laser light and a feedback mechanism 120 which detects a focusing position and always keeps the focusing position. The respective means are optically arranged so that the information of a Y picture element, an M picture element and a C picture element is simultaneously focused on the Y layer, the M layer and the C layer. Namely, owing to the action of such optical arrangement, the Y picture element, the M picture element and the C picture element are slightly deviated and simultaneously focused on the respective layers to arrange picture element information. Thus, the constitution is simplified and an inexpensive full color image forming device is obtained.