PURPOSE: To easily correct variations of every picture element in a photodetecting part, by writing variation information of every picture element in the second analog shift register, and correcting a signal from the first analog shift register utilizing of said information.

CONSTITUTION: The second analog shift register 4' is used, and variation information of every picture element at the point of time similar to a standard condition or a standard condition obtained at a part of the scanning period is directly written in this register 4', and also the written information is read out by synchronizing the picture element at every scanning to correct a signal obtained from the first analog shift register 4.