A CCD of a digital camera has high sensitive main pixels for depicting gradations in low and middle brightness portions of a subject, and low sensitive sub pixels for depicting gradations in high brightness portions of the subject. Main pixel image signals from the main pixels have a larger signal level than sub pixel image signals from the sub pixels. The main pixel image signals are attenuated by an attenuator to have the same signal level as the sub pixel image signals. The attenuated main pixel image signals and the sub pixel image signals are amplified by an amplifier with the same gain. The amplified main and sub pixel image signals are digitalized and composed to generate composite image data.