To solve the following problem: in a conventional image forming apparatus, when interpreting print job data D11 described in a PDL and generating an intermediate code D13a in a drawing execution part, it takes long to perform repetitive processing for dividing polygon drawing data 20 in the print job data D11 into many trapezoidal regions, comparing position relations between all the divided trapezoidal regions and a rectangular region 21, and determining a trapezoidal region to be drawn.

In an image forming apparatus 10, in an editing part 13, a first pre-processing part 13a for performing apex reduction processing which reduces unnecessary apexes for gradation drawing inside apexes of polygon drawing data 20 in advance is added before processing at a drawing execution part 13b. Thus, the number of trapezoidal regions created by dividing the polygon drawing data 20 decreases, and the number of times to compare position relations between the trapezoidal regions and a rectangular region 21 decreases, so that processing for interpreting print job data D11 described in a PDL and creating an intermediate code D13a is sped up.