PURPOSE: To detect the coordinate position with high accuracy by supplying an adverse current to a compensation loop to control the intensity of a magnetic field produced by a source line.
CONSTITUTION: A compensation loop 21 is provided along the source line 2s of a main loop 2m and the segment where a pickup 3 is positioned is detected for the detection of the rough position of the pickup 3. Then the compensating current value corresponding to the relevant segment is called out of a ROM table 24. Then the compensating current equivalent to the corresponding current value is supplied to the loop 21 in the direction adverse to the current sent to the line 2s. Thus a magnetic field produced on the line 2s is cancelled and the magnetic field is inverted at a prescribed position.