PURPOSE: To measure exactly the density of an original texture by detecting a prescribed value or above of the density of an original image having a specified width or above.

CONSTITUTION: The image exposing light by the light reflected from an original image or transmitted therethrough is irradiated to a recording body 6, by which the surface potential conforming to the original image is generated. The potential is detected by a sensor 10 and is subjected to integration processing, by which the density of the original image is detected and the density of the original texture is measured. When the prescribed value or above of the density of the original image that continues for a specified width or above is detected, the detected density of the original image is skipped and jumped via a clip circuit, etc. The original texture is thus exactly measured and the image having the adequate density is formed even if the original is copied while the original cover is held open or when the original has a black belt-like bold line.