To make it possible by using a single white lamp to improve an S/N ratio in image data of sensitivity characteristics (RGB) read with a CCD line sensor and to keep balance among the respective image outputs necessary for e.g., the function of forming a dropout color.

The monochromatic image data of RGB as dropout colors are required to be balanced among output levels. Therefore, the lighting of a fluorescent lamp is controlled to change the quantity of light impinging on a color CCD among the colors of RGB. Since the single lamp is used, its lighting is controlled so that the quantity of emitted light is balanced at the line period of the CCD. The control method used is one in which the duty of one light emitting cycle and the time of the lighting of the lamp per line is controlled according to the respective colors. Further, to cope with a long-term change (especially, light source change due to deterioration in a blue phosphor), the condition of control can be changed.