Charge is periodically supplied to a detection electrode so that a first alternating current voltage is generated in the detection electrode, and a detection signal corresponding to the supplied charge is created. A second alternating current voltage having the same frequency and phase as the first alternating current voltage is applied to a plurality of driving electrodes. An amplitude pattern, which is a combination of the amplitudes of the second alternating current voltages to be applied to the plurality of driving electrodes is switched according to a predetermined series of amplitude patterns. In each amplitude pattern included in the series of amplitude patterns, the second alternating current voltage having a certain amplitude is applied to the remaining driving electrodes resulting from excluding one driving electrode, and the second alternating current voltage having an amplitude different from the remaining driving electrodes is applied to the one driving electrode.