PURPOSE: To attain a copy having a white ground regardless of prevention of ground dirt and the color of the ground by detecting the ground density of an original with plural sensors.

CONSTITUTION: Detection information of sensors 3aW3e are inputted to a switch 4, an AD converter 6, and a CPU 5b of a microcomputer 5 and are stored in a memory 5c. Detected quantities of light due to sensors 3aW3e are compared with data X1 of a quantity of reflected light for absence of originals on a platen 1 and data X2 of a quantity of reflected light for an original information part is discriminated by the CPU 5b. Absence of originals is judged if detected quantities are larger than data X1, and presence of an information part is discriminated if they are smaller than data X2, and data which are smaller than data X1 and larger than data X2 are extracted, and the largest data out of extracted data is judged to be data of the ground of the original. This data is sent to a light quantity correcting device 7 of an irradiating light source.