PURPOSE: To obtain an installing fastener and the form of the leg of the installing fastener which can be installed to and removed from a support member simply and securely, by providing a claw which projects to the outer side of an insertion member, and can be pushed in to the insertion member elastically; and a sloped surface to give a moderation in the moving direction of the claw.

CONSTITUTION: An installing part 10 is pushed in to a through hole 32 by directing its inserting part in the direction of the arrow A. In the pushing in time, a claw 26 is deformed elastically by hitting its sloped surface 26B to the inner surface of the through hole 32. When the pushing-in amount reaches to a specific value, the claw 26 is opposed to a counter sunk hole 38, and the elastic deformation is released, the sloped surface 26C is engaged with a step 38A, and the installing part 10 and an installing piping 12 are installed securely. In order to remove the installing part 10, it is lifted upward, and after the sloped surface 26D of the claw 26 is hit to the upper end of the counter sunk hole 38 to give a moderation feeling, it is pushed in to an insertion member by an elastical deformation, and the claw 26 is removed from the counter sunk hole 38 so as to oppose to the through hole 32. The resistant force to pull out the claw 26 from the through hole 32 is eliminated, and the installing part 10 can be removed in the direction of the arrow A from the inside of the through hole 32.