From among plural receiver electrodes (6a to 6n) for receiving a transmission signal transmitted from transmitter electrodes (16a, 16b) of an intra-subject introduction device (2), receiver electrodes for receiving an image reception signal are selected by a receiver electrode selection circuit (18). Further, receiver electrodes for receiving a signal for position detection are selected by a receiver electrode selection circuit (21), from among the other ones of the plural receiver electrodes (6a to 6n) than the receiver electrodes selected by the receiver electrode selection circuit (18).