Contact Deciding Apparatus

A contact deciding apparatus includes: reference signal creating units that create first and second reference signals, with a sine wave, that have the same frequency as a detection signal output from a sensor unit, and are respectively in phase with and out of phase with the detection signal; a demodulation circuit that creates first and second demodulation signals by multiplying the detection signal respectively by the first and second reference signals; low-pass filters that extract first and second direct-current signals, which are respectively the direct-current components of the first and second demodulation signals; and a contact deciding unit that makes a decision about contact according to the first direct-current signal. The contact deciding unit decides that the connection state between the sensor unit and the detection circuit is abnormal when the first and second direct-current signals change in the same direction and normal when these signals change in opposite directions.