PURPOSE: To simplify a CAD input operation by displaying a screen having the same array of keys as a keyboard in addition to a CAD screen via a multi- window function and hitting the corresponding key on the screen by means of a tablet device and a stylus pen or a mouse.

CONSTITUTION: If it is required in a picture drawing mode to input the dimensional value, a pattern name, etc., a key array window opening instruction area 6 of a tablet device 4 is hit by a stylus pen 5. Thus a key array window 3 having the same array of keys as a keyboard is opened on a screen of a display 1. Then, when the corresponding key is hit by the pen 5, an input operation equal to the manual input operation performed via the keyboard is attained. As a result, all input operations are carried out on the screen with the pen 5 kept in a hand of an operator. Thus the operator is not required to holds and release the pen 5. As a result, a CAD input operation is simplified together with reduction of the input time. Then the physical fatigue is reduced for the operator.