To provide a flange coupling structure capable of easily connecting two piping members in one-touch and improving sealing performance.

A first flange coupling member 3 is mounted on a first piping member 1, and a second flange coupling member 4 is mounted on a second piping member 2. A first flange coupling member 3 includes a connecting male portion 32 forming an oval on an outside diameter, and an inserting hole 44 capable of inserting the connecting male portion 32 and a spot-faced hole 42 capable housing the connecting male portion 32 are formed on the second flange coupling member 4. A pair of interference portions forming a diameter smaller than the oval portion of the connecting male portion 32 are respectively formed at opposite positions with an arbitrary angle on the spot-faced hole 42. Upon turning the connecting male portion 32 at approximately 90° after inserting into the spot-faced hole 42, both flange coupling members 3 and 4 are joined so that the oval portion gets over the interference portion and the oval is connected with a wall portion around the spot-faced hole 42.