JPH0459667B

PURPOSE:To detect the abnormal light quantity at each part in the center line direction of a lamp by providing the white ground areas parallel to the main scanning direction at two areas in the subscanning direction within a raster scan area, e.g., at the two sides of an outer frame of an original platen which are parallel to the main scanning direction. CONSTITUTION:The white ground areas 9 and 10 are provided at low sides of an outer frame 2b of an original platen 2 which are parallel to the main scanning direction. Both areas 9 and 10 are set within a raster scan area, and the light quantity is detected by output of an image sensor 5 obtained by scanning the area 9 at each part in the center line direction of the lamp 3 and immediately before the reading job is started for an original 1. While the light quantity can be detected by the output of the sensor 5 obtained by scanning the area 10 for each part in the center line direction of the lamp 3 and immediately after the original 1 is read. These two types of light quantity are compared with each other to detect the fault of the lamp 3.