To provided an expansion anchor capable achieving required practical strength and bearing force at a small groove depth.

The expansion anchor 10 comprises an anchor bolt 11, a nut 12, a spring washer 13, first and second outer layer plates 151, 152, and first-fifth inner layer metal plates 161-165. The first and second outer layer plates 151, 152are each bent at an angle of elevation corresponding to a dovetail groove. The widths of the first-fifth inner layer metal plates 161-165are greater in order from the fifth to first inner layer metal plates 161-165. The upper parts of four side faces or all faces of the first-fifth inner layer metal plates 161-165are chamfered to be continuous faces at the same angle of inclination as that of the side wall of the dovetail groove when the first-fifth inner layer metal plates 161-165are superposed in the same direction.

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