PURPOSE: To enable high-speed plotting on a frame memory by simultaneously writing data on picture elements at the periphery of a specific picture element by using a memory controller which has a decoding function.

CONSTITUTION: A graphic controller (GC) 100 is used and the frame memory consists of four dual-port memories (memories 1-4). When graphic data to be written in a specific address (Xi, Yj) is outputted from the graphic controller 100, respective memory controllers (10a, 10b, 20a, 20b, 30a, 30b, 40a, and 40b) detect memory picture elements where the graphic controller 100 intends to write the data according to the specific address (Xi, Yj) and information that the graphic data has. Then the respective memory controllers (10a, 10b, 20a, 20b, 30a, 30b 40a, and 40b) write the same data on peripheral memory picture elements adjacent to the memory picture elements in addition to the memory picture elements.