Whether or not a received drawing instruction is an instruction which needs an arithmetic operating process with a background portion is discriminated. When it is determined that the received drawing instruction is not the instruction which needs the arithmetic operating process with the background portion, the drawing instruction is converted into a drawing command and transmitted to a printing apparatus, and the received drawing instruction is stored as intermediate data. When it is determined that the received drawing instruction is the instruction which needs the arithmetic operating process with the background portion, the intermediate data which relates to the received drawing instruction is extracted from the intermediate data stored by the storing step, a drawing command in which the arithmetic operating process of the received drawing instruction has been executed to the extracted intermediate data is formed and transmitted to the printing apparatus.