In a distal end portion of a flexible sheath which is inserted integrally with an ultrasound transducer array, cell collecting hole portions each including a through-hole which allows a distal end portion outer periphery and an internal space of the flexible sheath to communicate with each other is provided, an edge for specimen cutting is formed at an opening portion of an outer circumferential side of each of the cell collecting hole portions, and after the flexible sheath is caused to reach a lesion part or the like of a subject, specimen collection is performed without additionally inserting a biological forceps or the like into the flexible sheath, whereby a specimen of a target site such as a lesion part is reliably collected without unnecessarily increasing the number of times of insertion and extraction of an instrument into and from a body, and the burden on an examinee is reduced.