A photosensor with improved correction of image signals has a first photosensor portion including a plurality of photoelectric converting devices for reading an object and providing image signals thereof. A second photosensor portion includes a plurality of photoelectric converting devices and provides reference signals from light reflected from a reference member, or light received directly from a light source. Correction circuitry corrects the image signals from the first photosensor portion in accordance with the reference signals output from the second photosensor portion. Preferably, the photoelectric converting devices of the first and second photosensor portions are arranged in adjacent, parallel lines on the same substrate. Preferably, reference signals from the converting devices of the second photosensor are used by the correction circuitry to correct the electrical signals from substantially adjacent converting devices of the first photosensor portion. A single converting device of the second photosensor portion may be used to correct either one or more of the converting devices of the first photosensor portion.