The present invention is provided with: an implantation part, a housing part (34) being provided at the distal end thereof; an ultrasonic transmission/reception part for transmitting and receiving ultrasonic waves to and from an observation region, the ultrasonic transmission/reception part being provided inside the housing part (34); a cable (41) for transferring an electrical signal inputted to and outputted from the ultrasonic transmission/reception part; an insertion part (36) for causing the cable (41) to extend from inside the housing part (34), a slit (36s) being formed along an extension direction E in an external peripheral part of the insertion part (36); and a fitting member (37) fitted on the outer face (36g) of the external peripheral part of the insertion part (36) along the extension direction E so as to cover at least a portion of the outer face (36g).