To reduce the burdens of a software and a hardware and to improve image sensor performance by automatically adjusting the lightness of a screen by using a counter for counting a green pixel value in a CMOS image sensor.

A line number, the green pixel value, a prescribed critical value and a prescribed reference value are inputted to a data judgment part 400, the green pixel value is judged and count control signals pertinent to respective ranges are inputted to a counter part 410 provided with the counter corresponding to the control signals to be increased one by one. Then, the count value is passed through an addition and comparison part 420 and first and second final sums TOT1 and TOT2 are outputted. The first and second final sums TOT1 and TOT2 are compared in a control part 450 and an exposure adjustment rate RATE is obtained. Then, the next exposure time is calculated by multiplying the exposure adjustment rate RATE with the exposure time at present in an exposure time control signal generation part 460 and the next image is captured by the next exposure time control signal.