PURPOSE: To adjust the phase of a carrier signal impressed on the electrode line of a tablet with that of a carrier signal detected in a coordinate indication means and to set the detection of a detection signal from the tablet electrode line to be secure by adding a phase variable circuit for synchronizing the phase with that of the carrier signal detected in the coordinate indication means.

CONSTITUTION: Capacitance is connected between the electrode lines 6, 7 of the tablet 2 and the detection electrode of a stylus pen 10, and the carrier signal from the electrode near the detection electrode of the stylus pen 10 is detected. The signal is amplified in an amplifier circuit 12 through a band pass filter 11 and is guided to a synchronization detection circuit 13 in a signal processing means 3. The switch 19 of the phase variable circuit 16 is changed over by the detected carrier signal and a control signal which is transmitted from a control circuit 15 and which corresponds to a rough position, and a delay carrier which is phasesynchronized with the detected carrier is inputted to the synchronization detection circuit 13. Thus, the inputted and detected carrier is switched by a signal which is phase-synchronized with the detected carrier by a multiplier and it can be demodulated.