PURPOSE: To supply accurate reference information to an information reading sensor by providing a standard density pattern between the contact glass and contact glass holding frame of a copying machine body positioned above the stand-by position of the information reading sensor.

CONSTITUTION: Between the contact glass holding frame 1a and original setting surface of the contact glass 3 of the copying machine body 1 positioned above the home position of the information reading sensor, the standard density pattern 24 consisting of stepwise reference density parts from the lightest to the darkest part is provided with a pattern surface in contact with the contact glass 3, and this density pattern 24 is used for corrections of each information reading sensor. Consequently, the number of the standard information volumes is plural, so variance in the sensitivity among information reading sensors due to temperature drift and that in characteristics among sensors are corrected easily.