The apparatus is provided with an abnormality determination means for determining abnormality of the apparatus where two different combinations of two electrodes are selected from the three electrodes, an alternating-current voltage is applied to an electrode in one combination by the voltage-applying portion to measure a value of a current flowing to the other electrode via the dielectric body by electrostatic coupling, an alternating-current voltage is applied to an electrode in another combination out of the at least two different combinations by the voltage-applying portion to measure a value of a current flowing to the other electrode via the dielectric body by electrostatic coupling, and an abnormality of the apparatus is determined from the current values measured.