As referred to above, reference numeral designates bellows that is expansible in the left and right directions, the both left and right side edge portions of this bellows are fixedly secured to the top edge portions of the above described left and right side walls and , and the tip end portion of the above referred pressurized air feed pipe is mounted to {HEAD ~ a central portion} of {TAIL ~ the same bellows}  
As referred to above , reference numeral designates bellows that is expansible in the left and right directions , the both left and right side edge portions of this bellows are fixedly secured to the top edge portions of the above described left and right side walls and , and the tip end portion of the above referred pressurized air feed pipe is mounted to { HEAD ~ a central portion } of { TAIL ~ the same bellows }
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