An input device comprising: a selection circuit connected to a plurality of electrodes provided on a capacitive touch panel and arranged to selectively connect the plurality of electrodes ; a calibration resistor (R CAL ) connectable to the selection circuit ; a constant current source for supplying constant current to the plurality of electrodes and the calibration resistor (R CAL ); an A/D converter connectable to the selection circuit to measure capacitance of the plurality of electrodes and a measured value measured when the calibration resistor (R CAL )is connected; and a control unit arranged to control the selection circuit for the A/D converter to measure the capacitance of one of the plurality of electrodes and the said measured value measured when the calibration resistor (R CAL ) is connected, and arranged to determine a contact coordinate of a touch object on the touch panel by calculating a ratio of the capacitance to the measured value, wherein the said measured value measured when the calibration resistor (R CAL ) is connected, is measured with all of the plurality of electrodes disconnected, and the calibration resistor (R CAL ) is connected in parallel with the plurality of electrodes to the selection circuit ; and, wherein the control unit is arranged to control the selection circuit to disconnect the plurality of electrodes except the one electrode so that the A/D converter measures a first voltage of the one of the plurality of electrodes, and then to ground the plurality of electrodes except the one electrode so that the A/D converter measures a second voltage of the one of the plurality of electrodes, and arranged to compare the first and second voltages to determine whether or not a noise influence is present on a detection surface of the touch panel. a selection circuit connected to a plurality of electrodes provided on a capacitive touch panel and arranged to selectively connect the plurality of electrodes ; a calibration resistor (R CAL ) connectable to the selection circuit ; a constant current source for supplying constant current to the plurality of electrodes and the calibration resistor (R CAL ); an A/D converter connectable to the selection circuit to measure capacitance of the plurality of electrodes and a measured value measured when the calibration resistor (R CAL )is connected; and a control unit arranged to control the selection circuit for the A/D converter to measure the capacitance of one of the plurality of electrodes and the said measured value measured when the calibration resistor (R CAL ) is connected, and arranged to determine a contact coordinate of a touch object on the touch panel by calculating a ratio of the capacitance to the measured value, wherein the said measured value measured when the calibration resistor (R CAL ) is connected, is measured with all of the plurality of electrodes disconnected, and the calibration resistor (R CAL ) is connected in parallel with the plurality of electrodes to the selection circuit ; and, wherein the control unit is arranged to control the selection circuit to disconnect the plurality of electrodes except the one electrode so that the A/D converter measures a first voltage of the one of the plurality of electrodes, and then to ground the plurality of electrodes except the one electrode so that the A/D converter measures a second voltage of the one of the plurality of electrodes, and arranged to compare the first and second voltages to determine whether or not a noise influence is present on a detection surface of the touch panel. <EOS>