PURPOSE: To make it possible to safely use the title pipe even in the increased internal-external pressure difference by disposing a large diameter bellows around a small diameter bellows in double and controlling the pressure of the space between both bellowses to be an intermediate value between the internal pressure of the small diameter bellows and the external pressure of the large diameter bellows.

CONSTITUTION: At the one end of the title pipe, a small diameter bellows 1 is rotatably connected to a large diameter bellows 2 in a hermetic sealing manner by means of a spherical joint 3. Meanwhile, at the other end of the pipe, the small bellows 1 is connected to the large bellows by way of a flange 4. A space 5 thus formed between the bellows 2 and 3 is hermetically sealed, and is maintained at a specified pressure by control of fluid rate through a branch tube 6 provided on the side wall of the bellows 2. As a result, even in the increased internal-external pressure difference regarding both the bellowses 2 and 2, it is possible to relax the pressure difference and hence to use the flexible feed pipe with easy and safety.