PURPOSE: To shorten variable power processing time by performing a thickening processing to pictures prior to a reduction processing.

CONSTITUTION: When an instruction for the reduction processing is inputted from a keyboard 40, a CPU 10 executes a known line thickening processing to the pictures indicated by the picture signals of an original screen memory 60. For instance, the CPU 10 copies the picture signals of the original screen memory 60 to a thickening processing screen memory 90. Thereafter, the CPU 10 executes the thickening processing on the thickening processing screen memory 90. When thickened pictures are prepared by such processings, the CPU 10 prepares reduced pictures on a work memory 70. When it is assumed that the reduction of 1/2 is instructed from a user, the signal to be written on the first row and first column of the work memory 70 for which the reduction rate is 1/2 is the one stored in the storage address of the first row and second column of the thickening processing screen memory 90 and the signal to be written in the second column is stored in the first row and forth column of the thickening processing screen memory 90. The address information is stored in a coordinate transformation memory 80.