PURPOSE: To quickly execute photometry by a photometry device in the printing of a microreader printer.

CONSTITUTION: A photometry unit B composed of a mirror for photometry 14, an image forming lens 15, and a photometric sensor 16, can be taken in and out so that the mirror for the photometry 14 is located in a reader optical path in the vicinity of a projection lens 6 on an enlarging side at the time of printing, a projected luminous flux reflected by the mirror for the photometry 14 at the time of printing, is converged on the photometric sensor 16 by an image forming lens 15, and the quantity of light projected on a photosensitive drum 13 via a scanning unit A, according to the obtained photometric output, is adjusted by the voltage control of an illuminating lamp 1.