To provide a wheel operation signal generator which promotes early and low-cost implementation of an automatic steering system by using existing facilities to generate a wheel operation signal.

A range including white lines on a road is photographed by a CCD camera 1. This picture is displayed on a display device 4, and horizontal and vertical synchronizing signals are extracted by a synchronizing signal separation circuit 21. These synchronizing signals are counted, and both ends of scanning lines in the center of the picture frame are cut to digitally convert only a part including the white part by an A/D converter 22, and the result is subjected to threshold detection by a target detection circuit 26. Positions of the white line part extracted in this manner are counted by the clock obtained by dividing the horizontal synchronizing signal into 64, and this counted value is subtracted from value 32 corresponding to the frame center, and the result is taken as an error signal. This error signal is successively stored in an error data register 28, and the past error signal according with the speed of an automobile is selected and outputted by a data selection circuit 29.