Abstract: An anchor comprises an anchor bolt having a shaft and a bolt head, a spreading sleeve having spreading parts provided at a tip portion of a tubular body capable of being fitted on a tip portion of the shaft and a cone nut provided at its inner side a screw through hole to threadedly engage with the shaft. The shaft of the anchor bolt is composed of a thick shaft part connected to the bolt head, and a thin shaft part provided to be closer to the tip portion of the shaft. The thick shaft part is provided with a rupture portion reduced in diameter. The rupture portion is provided at a position spaced by a predetermined length from the step between the thick shaft part and the thin shaft part and ruptures if torque of a predetermined value acts on the bolt head.