PURPOSE: To provide an inexpensive printer with a higher speed and a high reliability by arranging a light source, a slit, a liquid crystal panel and an SELFOC lens on the straight light.

CONSTITUTION: Light projected from a fluorescent tube (K) which is kept at a fixed temperature with a temperature controller (u) and a lamp heater (s) connected to a temperature sensor (t) while adjusted to a fixed brightness per unit area with a brightness sensor (q) enters a liquid crystal panel (a) passing a release port provided on a light shield plate (O). The panel (a) is filled with a nematic liquid crystal which is positive by a low frequency while negative by a high frequency depending on a cross frequency zero in the dielectric anisotropy between upper and lower substrates so arranged to intercept light with a polaroid element in adjusted direction of the polarization axis while the liquid crystal material is almost parallel to the substrates by horizontal orientation thereof is kept at a fixed temperature with a heater controller (g) connected to a heater sensor (h). Light only required for printing is passed by opening or closing a light valve section and projected on a photosensitive drum with an SELFOC lens (m).