The invention is intended to reduce the number of parts constituting an image capturing system using a solid-state image sensor and reduce the size and cost of a mobile electronic appliance having camera functionality. An analog front end circuit for an image capturing system, which samples pixel readout signals input from a solid-state image sensor, amplifies the sampled signals up to a predetermined level, and converts the amplified signals into digital signals, is formed, together with a DSP for digital image processing and a CPU responsible for arithmetic processing and control for camera functionality such as auto focusing and register setting, in a semiconductor integrated circuit on a single semiconductor chip.