PURPOSE: To improve the picture quality, by obtaining and storing a compensation coefficient from optical information from a uniform reflecting plane before reading an original picture and compensating the picture signal of original with the stored content at original reading.

CONSTITUTION: At the end of shading compensation coefficient storage with a stop signal from a control circuit 8, switches S1∼S4 are all selected from contact (a) to (b). While a start signal is outputted, two shading compensation coefficients are read out from a storage circuit 15 and processed for operation at an interpolation circuit 18. The shading compensation coefficient outputted from the circuit 18 is subjected to analog conversion at a D/A converter 11 and operated at an operation processing circuit 12 with an original reading signal from a sample hold circuit 10 and a signal V8 after compensation is outputted. Since the shading compensation is made with the interpolation method through the use of the compensation coefficient in reading the original picture, the fluctuation of the light distribution characteristics of a lamp due to time aging and temperature change can suitably be compensated, allowing to improve the picture quality.