To prevent deterioration of throughput by judging whether a predicted memory amount is effectively secured or not at the time of pre-rendering processing when a banding processing is impossible and selecting an optimum compressing method.

A rendering circuit 507 executes plotting processing on a hand memory to be secured on a work area 503A. CPU 506 executes a control program stored in ROM 502 and an external memory, etc., and secures it. A CPU 506 executes the control program stored in ROM 502 and the external memory, etc., and selectively processes it based on the secured result. In this case, a compressing/expanding circuit 508 executes compression of a bit map image which is plotted by a method where compression is executed in a min. time based on a comparison considering quantity with a compression time among the plural different compressing methods. Therefore, the optimum compressing means is selected in accordance with the memory area to be secured and the optimum compression is efficiently executed to plotting data in accordance with memory environment.