A bottom part (102) forming an annular packing holding part (H1) is disposed at the lower-end side of a cylindrical barrel part (101), between the lower-end side and the inner peripheral surface of the cylindrical barrel part (101). An annular packing pusher (103) is attached to the bottom part (102) so as to push an annular packing (104), which is held by the annular packing holding part (H1) between the inner peripheral surface of the cylindrical barrel part (101) and the outer peripheral surface of the bottom part (102), from below using the upper end of the annular packing pusher (103). From among a plurality of flange parts (102a, 102b, 102c) provided along the entire periphery of the outer peripheral surface of the bottom part (102) and with gaps therebetween in the vertical direction, the annular packing (104) is brought into contact with the lower surface of the lowermost flange part (102c), and the upper end of the annular packing pusher (103) pushes the annular packing (104), whereby the annular pac
