Abstract: A device for holding and securing a rotating tool to be attached to the spindle shaft of a machine tool, that can realize ultra-precise cutting or grinding work under conditions of high rotation speed and rapid feeding. A tool holder consists of an outer cylinder having a tapered outside peripheral surface which comes into contact with the inside peripheral surface in a tapered hole of a spindle shaft; an inner cylinder which fits in such a manner that the outer cylinder can slide in an axial direction; a retainer having an outer armor which is formed at the front end of the inner cylinder and can contact the top end of said spindle shaft; and an elasticity-accelerating member which imparts elastic force to the retainer such that the outer cylinder can move towards its base end.