PURPOSE: To reduce the capacity of a desired memory and also to attain a high- speed discriminating action by binary coding the read data on a prescribed original area with two threshold values different from each other and giving a logic operation to the obtained binary coding data to discriminate whether the original area is equal to a binary area or a half-tone area.

CONSTITUTION: An original 3 put on the contact glass 3 is exposed by a light source 1, and the reflected light of the original 3 is led to a CCD line sensor 6. Then the output of the sensor 6 is applied to an area discriminating part 7. The part 7 converts the output signal of the sensor 6 into the digital data by an A/D converter 8. This digital data is supplied to comparators 9 and 10, and the binary coding signals of both comparators are applied to an exclusive OR gate 11 to obtain an exclusive OR between both binary coded signals. The "1" level signals obtained during said processing are counted by a counter 12, and the count value of the counter 12 is applied to a comparator 13 to be compared with the reference value. Then a binary area or a half-tone area is decided according to the 0 or 1 level of the output signal of the comparator 13.