PURPOSE: To turn even a straight line expressed in the inputted coordinate data into another straight line free from any difference of levels in its grater part by securing the relative movement between a drawing setting board and a coordinate detecting substrate set under the drawing setting board.

CONSTITUTION: When a touch of a pen is secured to an axis correcting function key 13, a pen switch 30 produces a signal SW. A CPU 38 supplies an address signal to a decoder driver DD 42 in response to the signal SW and also supplies the scan pulses to the X and Y direction electrode wires 31 and 32 and the circular electrodes 15 and 16 respectively to decide a pen touching position then. Then a fact that an axis correcting function key is coincident with the pen touching position is detected from the timing when an induction pulse is produced at a tip 34 of an input pen 33. Thus a prescribed axis correcting subroutine is carried out. Then it is possible to detect the twist of the coordinate axis of a coordinate detecting substrate 3 and the coordinate axis of the drawing set on a drawing setting board. Then the substrate 3 is turned by an extent equivalent to the detected twist values of those coordinate axes.