A recess and an attachment seat are formed in a front end of a tool body. A panel-shaped insert attached to the attachment seat where the thickness direction is matched with the diameter direction of the tool body and a surface of the insert facing the rear in a tool rotation direction becomes a pressed surface. A peripheral cutting edge is formed at a ridge of an inclined surface on the outside in the diameter direction of the tool body, a bevel edge is formed at a ridge on the front side of the tool body, and a back taper is attached to the peripheral cutting edge. A pressing member for pressing the pressed surface of the insert to adjust a position of the peripheral cutting edge in the diameter direction of the tool body is disposed on the rear side of the attachment seat in the tool rotation direction.