PURPOSE: To make the reader small and to reduce the manufacture cost by converting a parallel color signal into a serial color signal and processing the converted signal so as to reduce the circuit scale and the size of a printed circuit board.

CONSTITUTION: The reader is provided with a three-line color CCD sensor 1, analog processing circuits 2a-2c, a selector 3, a control circuit 4, an A/D converter 5, a digital processing circuit 6 and an upper/lower, reference processing circuit 7. Then a parallel color signal outputted from the three-line color CCD sensor 1 is converted into a serial color signal by using a selector 3 synchronously with a scanning synchronizing signal to keep high speed performance of the three-line color CCD sensor 1 and to allow the use of one system of the A/D converter 5 and its peripheral circuit 6. Since one system of the A/D converter 5 is in use, the dispersion in the characteristic of the A/D converter 5 is prevented. Thus, the circuit scale is reduced, the manufacture cost is decreased and the high speed performance being a feature of the three-line color CCD sensor is maintained.