Included are a cylindrical holding portion 51, a groove 51m engageable with a balloon band removed from an outer periphery 30g of an ultrasound transducer unit 30, cut portions S that cut the holding portion 51 from one end 51p to the other end 51q, a fitting portion 60 that radially contracts an inner peripheral face 51n of the holding portion 51 from the other end 51q toward the one end 51p and includes a member that can radially expand in a radial direction K, and abutment portions 51 af to 51df that project inward in the radial direction K from the inner peripheral face 51n so that an end portion on the one end side of the fitting portion 60 abuts against the abutment portions 51 af to 51 df.
