PURPOSE: To simplify the operation, by changing arbitrarily the position and size of a cursor on a square and magnifying or shrinking the symbolic diagram having the corresponding size.

CONSTITUTION: A symbol after registration is selected at a symbol selection switch SW, the data is applied from a data base RSB to a symbol generator SRG and the symbol information is obtained. The symbol is displayed in a cursor CSR on a display screen DSP via a diagram storage device GPM. The position of the cursor CSR is shifted to the position of the white arrow by using a cursor position register CPR by means of a joy stick JS1. In the point, the lateral and vertical sizes are changed by a joy stick JB2. As a result, the symbolic diagram is changed for the position and size in the range indicated, by the cursor for display.