An inner tube is provided with a protruding portion protruding from an outer peripheral surface of the tube, in a position extending throughout the entire area of the outer peripheral surface of the tube, in a region located outside an outer tube, of the entire area in a longitudinal direction of the inner tube inserted into a through-hole of a discharge side wall of the outer tube, and the protruding portion of the inner tube is pressed by an outlet joint toward the discharge side wall along an axial direction of the outer tube, and thereby, the inner tube is cantilevered by the discharge side wall.