PURPOSE: To reduce an area discrimination processing time by discriminating whether or not a coordinate position corresponding to coordinate position information read by an area discrimination means is in existence in a designated area sectioned by a locus.

CONSTITUTION: An original placing port 102 is used to enter a locus of an area and its locus discrimination data is stored in a bit map memory 111. Locus discrimination data A0 for each coordinate and locus discrimination data A1 read just precedingly are read. Moreover, main scanning area data A2 whose value is kept as it is till locus discrimination data representing a succeeding locus are read in the main scanning direction, the preceding line locus discrimination data A3 being locus discrimination data of coordinate position in the same main scanning direction at one preceding line and locus discrimination data representing locus are read. In this case, whether or not a coordinate position corresponding to the data A0 in a discrimination block of an area changeover 112 is within the designated area is discriminated based on the line area data A4 whose value is kept as it is in the coordinate position in the same main scanning direction.