Analog pixel signals, which are read out from an image sensor, are subjected to predetermined signal processes, and are converted to digital pixel signals by an A/D converter. The digital pixel signals are separated to RGB signals. The RGB signals are multiplied by a predetermined color matrix coefficient. After that, luminance signals are extracted from the RGB signals. A light adjusting control signal for adjusting the quantity of light is calculated based on the luminance signals. The color matrix coefficient is changed based on the light adjusting control signal.