To provide a novel flexible rubber joint and its mounting structure and its constructing method.

The flexible rubber joint 10 is arranged along a connection portion of a can. It comprises an integral unit formed by a flexible curved portion 11 ranging in the longitudinal direction, a pair of bottom plate portions extending from its bottom and ranging in the longitudinal direction and a pair of side wall portions 13 extending from its end to a direction y of protrusion of the curved portion and ranging in the longitudinal direction. The flexible rubber joint 10 is used with both longitudinal ends tied to each other in the form of a ring using a top 11a of the curved portion as the inside thereof. Self-supporting rigidity is granted to the ring by pressure plates 21 mounted along the peripheral direction, a connection plate for fixing the adjacent pressure plates 21 to each other, a space holding material for fixing an angle formed by the pair of bottom plate portions 12 and a reinforcing material for retaining the shape of the whole ring.