A post-installed anchor by which high drawing strength can be reliably maintained and an anchoring operation can be stably performed, or the like. A post-installed anchor, which is anchored into an anchor hole having a diameter expansion portion, includes: an anchor main-body inserted in the anchor hole; a plurality of straight-shaped guide opening portions formed to penetrate in a radial direction at positions corresponding to the diameter expansion portion; a plurality of spread pieces slidably provided at the respective guide opening portions and engaged to the diameter expansion portion in an anchoring state in which the plurality of spread pieces spread in the radial direction; and a cone portion that slides the respective spread pieces to an outside in the radial direction to spread the plurality of spread pieces.

To provide a method for forming an anchor hole and a diameter expansion device by which a centrifugal force can be appropriately adjusted when a cutting-blade portion is moved in a radial direction by the centrifugal force to grind a diameter expansion portion. In a method for forming an anchor hole for a post-installed anchor in which a diameter expansion drill bit is inserted and rotated in a prepared-hole portion bored in a concrete fixing body and a cutting-blade portion of the diameter expansion drill bit is moved in a radial direction by a centrifugal force to grind a part of the prepared-hole portion to form a diameter expansion portion, the minimum value of the centrifugal force applied to grind the diameter expansion portion is 0.75 N and preferably 1.1 N.

A device for forming a diameter-enlarged hole portion by cutting into a hole that is formed in a workpiece, the device including: a bow jaw including a shaft and a guide, the guide including a distal end surface and an sloped surface, the distal end surface being provided on an opposite side of the guide from the shaft, the sloped surface being sloped from the shaft side of the guide toward the distal end surface side of the guide in a direction away from a center axis of the shaft; and a cutter blade including a cutting portion whose distal end is provided with a cutting edge, the cutting portion being slidable along the sloped surface. The bow jaw further includes a suction passage that includes a flow passage, the flow passage including a suction port that is open at the distal end surface.