To provide a butterfly valve secured in sealing performance by preventing a gap between a seat ring and a stem, and improved in durability by reducing the twisting of the seat ring caused by the rotation of the stem.

In the butterfly valve, the seat ring 3 is attached in a short cylinder shaped body 2, and a valve element 5 is rotatably provided in the seat ring 3 via the stem 4. An attachment groove 11 is formed at an outer peripheral edge 13 of a stem through hole 10 formed at the seat ring 3, a ring 20 of a backup ring 6 is attached to the attachment groove 11, a protruding part 21 is protrusively formed at an upper outward part of the ring 20, a bearing face 22 is formed at a stem through hole 10 side of the protruding part 21, an engagement face 23 is formed at an opposite side of the bearing face 22, the engagement face 23 is engaged with a step face 16 formed at an inner circumference side of the body 2 in a state of carrying out the sealed retainment of the stem 4 in the stem through hole 10 when the valve element 5 is pressurized by fluid pressure and the stem 4 is moved in a pressurization direction, and the stem 4 is borne by the bearing face 22.