PURPOSE: To eliminate uneven exposure, etc. with respect to an original, by deriving each coefficient which is derived from a use elapsed time and use frequency, and correcting automatically photodetecting sensitivity of a CCD type line sensor in case of that time point.

CONSTITUTION: An output of a CCD type line sensor 1 is digitized by an A/D converter 2, this value is collated with a data from a correcting and calculating device, and it is outputted as a picture through a D/A converter 4. This value is collated with a data from the correcting and calculating device 3, and it is outputted as a picture through the D/A converter 4. The correcting and calculating device 3 calculates a correcting value by use of a sensitive curve of the CCD type line sensor and its curve for deterioration with age, which are prescribed in advance.