PURPOSE: To improve the processing performance by setting a register value according to an original size to be read and applying a coincidence signal output resulting the comparison of a comparator to a CPU.

CONSTITUTION: At first a CPU 1 sets the number of subscanning signals to a register 2 when the length (y) of an original G is scanned by a scanner S and a counter 3 counts the subscanning signal outputted from the scanner S when being moved in the subscanning direction (in the direction of arrow). Thus, as soon as a carriage mounting a sensor of the scanner S finishes the scanning of the original G, the content of the register 2 and the counted value of the counter 3 are coincident. That is, the coincidence signal is interrupted from a comparator 4 to the CPU 1 to make the input of a picture data to a personal computer complete. In this case, the scanner S applies the remaining scanning of the readable range although no picture data is outputted. The succeeding data processing is attained without waiting for the end of the scanning of the scanner S.