PURPOSE: To reduce the capacity of a desired memory and to attain high-speed discriminating action by binary coding the read data on a prescribed original area with threshold values different from each other and counting the number of 1 and 0 levels of each binary coding data to discriminate whether the original area is equal to a binary area or a half-tone area according to the difference between the counted 0 and 1 levels.

CONSTITUTION: An original 3 put on the contact glass 2 is exposed by a light source 1, and the reflected light sent from the original 3 is led to a CCD line sensor 6 via a mirror 4 and a lens 5. An area discriminating part 7 converts the output signal of the sensor 6 into the digital data by an A/D converter 8 and applied to comparators 9 and 10 to which different reference levels are applied. Then the "1" level signals sent from both comparators are counted by counters 11 and 12 respectively, and the counted values of both counters are supplied to a subtractor 13 to obtain a reduction amount. This amount is applied to a comparator 14 and compared with the reference value applied previously. 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 14.