PURPOSE: To form an air chamber and a communicating part as a large-diameter part is fixed to the inner peripheral surface of a tube main body so as to simplify a pressure regulating mechanism by forming a cover member for forming the pressure adjusting mechanism out of a plate material comprising a large- diameter part and a small-diameter part.

CONSTITUTION: A filler part 33 is formed on an opening part of a tube main body 31, and the filler part includes an inner flange 33a and a click part 33b. A pressure regulating mechanism 35 is disposed on the filler part 33, and the mechanism is formed by disposing a cover member 37 on the tube main body 1. In this case, the cover member 37 is formed by forming a plate piece like a circular-arc and connecting a small-diameter part 37a and a large-diameter part 37b to each other by a stepped part, and the small-diameter part 37b is brought into contact with the inner flange 33a. The large-diameter part 37a is spot-welded on the tube main body 31. A breather hole 31a is formed in a position of the tube main body 31 that is opposite to the small diameter part 37b. Thus, an air chamber and a communicating part 41 are formed by the small-diameter part 37b, the tube main body 31 and the filler part 33.