In order to provide a tool holder which greatly reduces frictional resistance between a locknut and a taper collet, and eliminates a twisting of the taper collet during tightening of the locknut, in a tool holder comprising a locknut 13 which pushes a taper collet 12 into a tapered hole 115 of a collet chuck body 11 to chuck a cutting tool 15, between a reference end 123 of the tape collet 12 and a collet supporting portion 131 opposed thereto, interposed is a bearing washer 14 to reduce frictional resistance between both contact surfaces. To both surfaces of this bearing washer 14, namely, to the respective surfaces which come into contact with the reference end 123 and collet supporting portion 131, surface treatment by any of ion nitriding, DLC (Diamond-Like Carbon) coating, and TiN coating is applied.