A signal processing circuit for connection to one (11 X i) of a plurality of signal receiving conductors (11 X 1 - 11 X 72) of a capacitive position detecting sensor, the signal processing circuit comprising: a clamp circuit including a switch circuit; a gate circuit; a capacitor circuit; a gate control circuit; and an analog digital converter connected to one terminal of the capacitor circuit and configured to output the change in capacitance corresponding to the position of an indicator on the capacitive position detecting sensor in form of a digital signal; wherein one terminal of the gate circuit is connected to one terminal of the clamp circuit (31a, 31e), said terminals being connectable to the one signal receiving conductor (11 X i) of said plurality of signal receiving conductors (11 X 1 - 11 X 72); wherein the one terminal of the capacitor circuit is connected to the other terminal of the gate circuit, and wherein the other terminal of the clamp circuit (31a, 31e), the other terminal of the capacitor circuit, and optionally further the analog digital converter, are coupled to the predetermined potential ( V ref); wherein, when connected to the one signal receiving conductor (11 X i), the signal processing circuit is adapted to set said one signal receiving conductor (11 X i) to the predetermined potential ( V ref) via the clamp circuit and to connect said one signal receiving conductor (11 X i) to the capacitor circuit via the gate circuit based on conduction control of the gate circuit by the gate control circuit; characterized in that the gate control circuit is adapted to carry out conduction control of the switch circuit prior to the conduction control of the gate circuit to keep the one signal receiving conductor (11 X i) at the predetermined potential ( V ref) for a predetermined time period; wherein a conduction control overlapping period is set in which the conduction control of the switch circuit and the conduction control of the gate circuit are each carried out; and wherein the signal processing circuit is driven by a single power supply voltage ( V cc) and the predetermined potential ( V ref) is set to one half of the single power supply voltage ( V cc). a clamp circuit including a switch circuit; a gate circuit; a capacitor circuit; a gate control circuit; and an analog digital converter connected to one terminal of the capacitor circuit and configured to output the change in capacitance corresponding to the position of an indicator on the capacitive position detecting sensor in form of a digital signal; wherein one terminal of the gate circuit is connected to one terminal of the clamp circuit (31a, 31e), said terminals being connectable to the one signal receiving conductor (11 X i) of said plurality of signal receiving conductors (11 X 1 - 11 X 72); wherein the one terminal of the capacitor circuit is connected to the other terminal of the gate circuit, and wherein the other terminal of the clamp circuit (31a, 31e), the other terminal of the capacitor circuit, and optionally further the analog digital converter, are coupled to the predetermined potential ( V ref); wherein, when connected to the one signal receiving conductor (11 X i), the signal processing circuit is adapted to set said one signal receiving conductor (11 X i) to the predetermined potential ( V ref) via the clamp circuit and to connect said one signal receiving conductor (11 X i) to the capacitor circuit via the gate circuit based on conduction control of the gate circuit by the gate control circuit; characterized in that the gate control circuit is adapted to carry out conduction control of the switch circuit prior to the conduction control of the gate circuit to keep the one signal receiving conductor (11 X i) at the predetermined potential ( V ref) for a predetermined time period; wherein a conduction control overlapping period is set in which the conduction control of the switch circuit and the conduction control of the gate circuit are each carried out; and wherein the signal processing circuit is driven by a single power supply voltage ( V cc) and the predetermined potential ( V ref) is set to one half of the single power supply voltage ( V cc).