PURPOSE: To prevent picture quality from deteriorating by detecting the amount of signal change based on a chrominance signal and the average color signal of this color and correcting the brightness of the average value chrominance signal of the other color by using the change amount.

CONSTITUTION: Original picture information read after photoelectric conversion by a CCD line sensor 1 is corrected in a shading correction circuit 3, turned to be a digital signal in an A/D conversion circuit 4, and inputted to a color separation circuit 5. An R signal outputted from the circuit 5 is inputted to shift registers 13 and 14 in order. When the R signal inputted to the register 13 is for the noted picture element, the R signal before one picture element is in the register 14, and the R signal with one picture element is obtained from the circuit 5. The average value R signal with three picture elements is obtained by the arithmetic circuit 19, and the noted picture elements and the average values of B and G signals are similarly obtained. Further, the ratio of the G signal of the noted picture element and the average value G signal calculated by an arithmetic circuit 20 is obtained. The picture quality is improved by correcting the signal ratio by proportionating it to the average value R signal in the arithmetic circuit 23.