PURPOSE: To directly measure a reflection factor from an original, by installing a reflection factor measuring instrument for measuring a reflection factor of an original placed on a platen, to a platen cover provided on the platen so as to be freely openable and closable.

CONSTITUTION: On the lower face of a housing 6 of a reflection factor measuring instrument 5 incorporated in a platen cover 4, a through-hole 6a is provided, light from a light emitting element 7 in the housing 6 is projected to the upper face of an original 2 through the through-hole 6a, and its reflected ray is photodetected by a photodetector 8. In general, the original 2 is placed on a platen 3 with its copying face down, but the reflection factors of the upper and lower faces are almost same, therefore, by photodetecting the reflected ray reflected by the upper face of the original 2, by the photodetector 8, the reflection factor of the original 2 can be fetched as an electric signal. The reflection factor of the original 2 detected by the photodetector 8 is inputted to the control system, and the light quantity of the exposure lamp, the charging quantity, the developing bias, etc. are controlled.