A shank attaching structure with as less axial free movement as possible and of a simplified construction, a cutter for use with the shank attaching structure, and a cutter for use with the shank attaching structure which is free from an incident that the cutter becomes incapable of coming off even if an impactive rotating torque is exerted thereon, are intended to be provided, wherein the shank attaching structure is constructed such that in a state restricted by a restriction mechanism for restricting a depth to which a shank (7) is inserted into an arbor (A), the position of an engaging portion (7B) relative to the lock member (5) is axially deviated toward the open side of a shank attaching bore to bring the lock member (5) and the engaging portion (7B) into abutment with each other on the base end side of the shank attaching bore. The cutter (B) is constructed such that an outer peripheral edge portion (7C) of a concave portion forming the engaging portion (7B) is dented from an outer peripheral surface of the shank (7).