PURPOSE: To perform the addition processing of two scanning line data while reducing the number of adders at the time of compressing the number of scanning lines of a video signal.

CONSTITUTION: Based on the data of bit K1 of one decimal digit and the data of bit K4 of four decimal digits, the data of a scanning line Ln or scanning line L(n+1) are selected by selectors 1-4. A selector 8 selects the data of a scanning line L(n+1) based on the above mentioned K4. The data from the selectors 1-4 are added by adders 5 and 6. The data from the adders 5 and 6 are added by an adder 7. The data are added to an adder 9, then added with the data from the above mentioned selector 8 to generate a scanning line Ln' and to output the result.