PURPOSE: To realize small size, low noise, and high speed of the titled printer, and to improve the printing quality by utilizing a switching effect of total reflection and transmission generated by a variation of a refractive index by injecting a carrier, as a switch array.

CONSTITUTION: Beams from plural pieces of semiconductor lasers 1 are condensed by a lens optical system 2 containing a cylinder lens, and each point of an optical switch 3 is irradiated. The beam which has been brought to a waveguide in the optical switch is brought to an image formation on a photosensitive drum 5 by a SELFOC array lens 4. The optical switch array 3 is brought to a dot formation in parallel to every one line of printing. The optical switch array 3 is driven by a parallel driving circuit 6. The printing density is determined by the number of elements of an optical switch array. With regard to one element of the optical switch array, the light beam is made incident on a waveguide 11, and made to reach a carrier injection area 12. In case no current is injected to this area 12, the light is brought to a total reflection, and when it has been injected, a refractive index decreases and the light beam transmits. According to this system, a small size, low noise, and high speed of a printer are realized, and the printing quality is improved.