An image processing apparatus easily and reliably realizes complicated 1-line processing by a simple method, and controls accumulation period for respective colors without any particular function such as shutters on the line sensor side. One line period is divided into a reading section for reading valid image data, a dummy section for sweeping electric charge accumulated in the reading section and for synchronization, and a section for setting accumulation periods for the respective colors. In the reading section, the line sensor is driven by a necessary transfer frequency, and in the other sections, the sensor is driven at a high speed.