PURPOSE: To make an information recording device applicable to both a stationary exposure system and a slit exposure system, to preclude a decrease in resolution, and to omit a pre-scan and shorten the time up to fast copying by controlling the concentration adjusting means of a printer part according to the difference between the output of a reflected light detecting means and an external light detecting means.

CONSTITUTION: A sensor 16 which detects projection light reflected by the diffusion surface 10a of a screen 10 is provided nearby a screen 10 and a sensor 17 which detects external light incident on a reader part after it is transmitted through the screen 10 and diffusion surface 10a is provided on the diffusion surface 10a. A differential amplifier 20 finds and amplifies the difference between the output of the sensor 16 and the output of the sensor 17 and a power control circuit 22 drives an illumination lamp 2 as the concentration adjusting means according to a control signal. A high voltage transformer 23 varies the bias voltage of a developing sleeve 24 as a concentration adjusting means. The difference signal corresponds to the actual quantity of the projection light, so it is measured without prescanning to adjust the concentration automatically.