To provide an expanding anchor requiring little energy, preventing the applied finish coating from being damaged during the movement of an expanding main body, and capable of avoiding the ordinary-temperature welding of a stainless material.

This expanding anchor is provided with an expanding sleeve 2 constituted of a through hole 9 extended in the axial direction and an expanding region 3 having at least one longitudinal slit 5 and an expanding main body 6 movable from the initial position to the final position in the axial direction in the through hole 9 when the expanding region 3 is expanded. The radius of curvature (a) of the inner face of the through hole 9 adjacent to the peripheral face 7 of the expanding main body 6 is made substantially coincident with the radius of curvature of the peripheral face 7 of the expanding main body 6 on the cross section of the position where the expanding main body 6 is located at the final position.