PURPOSE: To hold information at the time of storage even when the information is called again by visually display image data and then having a graph mode changing means even after the display.

CONSTITUTION: When an XY chart is indicated, the XY chart is held in a graph kind storage part. Then whether a connection is made by a curve or straight line is selected. Once the curve or straight line is specified on a keyboard 4, its information is written in the graph kind storage part in a main memory 3. Then information on eight selected cells is written in the graph structure storage part in the main memory 3 by process communication. The graph structure storage part including the graph kind storage part and series information storage part in the main memory is developed on an image memory 6. Here, when a display mode setting change is indicated on the keyboard 4, a display mode setting process is performed.