To easily and certainly conduct flange joining ensuring a sealing property.

This flange joining packing 10 includes an inner space 16, a viscous substance 18 filled in the inner space 16 and a viscous substance passage 20. When a prescribed or necessary fastening force is applied on the packing 10 from flanges 12, 14, the inner space 16 is compressed to lead out the viscous substance 18 to an outside collecting portion 36 through the viscous substance passage 20. The viscous substance 18 is collected to expand the collecting portion 36 and a projecting portion 34. By confirming that the viscous substance 18 moves to the outside, it can be easily confirmed whether prescribed fastening torque is added or not.