PURPOSE: To always obtain image pickup signal of a constant level even when variation in the quantity of light occur in the light source, by compensating the output from the photoelectric conversion section for image pickup or the quantity of light of the light source with the output of the reflected light detecting section.

CONSTITUTION: Image pickup is started after an origianl is placed on an original placing table 1 and a fluorescent lamp 3 is turned on. Pictures of the original and reflected light from a reflecting body 2 are absorbed into a photoelectric transducer 5 for image pickup through optical systems 4 and 4', and are outputted from the element 5 after they are photoelectrically converted into image pickup signals. The output from the photoelectric transducer 5 is supplied to an input terminl 6 of an image pickup signal compensating circuit. On the other hand, a control signal is impressed upon a control input terminal 11 and an analog switch SW of a sample holding circuit is closed. Thus a closed loop is formed including a variable amplifying section 8, and the gain of the variable amplifying section 8 is set in such a way that the output voltage which appears at an output terminal 12 becomes the same in level as the comparison voltage VF of a comparison amplifier 9.