PURPOSE: To perform a graph processing by a rememberable grammar without requiring much labor by an image that a man uses a pen and paper when the graph is plotted by a man-machine interface at the time of utilizing a computer.

CONSTITUTION: A plotting unit 10 is composed of an object control part 1 and a command interpretation part 2. The object control part 1 controls objects of pens and plotting paper and the command interpretation part 2 starts the attributes of these objects and outputs a required Xlib command when a command to plot data, for instance, is delivered. As for the objects, for instance, the pens ate provided with colors, types, ranges, etc., and the plotting paper is provided with width, height, measure width, etc., as the attributes. These pens and plotting paper can be generated by a desired number and can be controlled by endowing them with names.