A housing is provided with an internal space for accommodating an insert and a cylindrical cap attachment part provided, at the distal end surface thereof, with an opening part communicating with the internal space. An inclined groove that is inclined from the distal end side to the proximal end side of the cap attachment part along the circumferential direction of the cap attachment part is provided on the outer circumferential surface of the cap attachment part. A cap fixing part for attaching a seal cap to the cap attachment part has a cap holding part for holding the outer peripheral surface of the seal cap and an elastic part connected to the cap holding part. The elastic part is provided with a protrusion that is fit into the inclined groove of the outer peripheral surface of the cap attachment part.