A tool chuck comprising: a collet for gripping a tool ; a chuck body having, at a leading end thereof, a receiving portion for receiving the collet inserted therein along an axis (AX) thereof; a holder containing the collet therein and configured to be movable together with the collet along an axial direction; a nut (N) fitted on the chuck body and containing the holder ; and the holder having a movement allowing mechanism for allowing the holder to move relative to the nut (N) along the axial direction (x) when the nut (N) is moved relative to the chuck body along the axial direction; wherein the holder includes a first holder member contained in the nut (N) and a second holder member contained in the first holder member and containing the collet ; the first holder member and the second holder member are movable relative to each other along the axial direction (X); the first holder member and the second holder member are formed annular about the axis (AX); the movement allowing mechanism includes an engaging protruding portion provided in one of the first holder member and the second holder member along a circumferential direction relative to the axis (AX) and an engaged receding portion provided in the other of the first and second holder members along the circumferential direction and engageable with the engaging protruding portion ; characterized in that the engaging protruding portion is elastically deformable in the radial direction (R); and the engaged receding portion includes a pair of small receding portions provided side by side along the axial direction (X) and holding the engaging protruding portion and a protrusion provided between the small receding portions . a collet for gripping a tool ; a chuck body having, at a leading end thereof, a receiving portion for receiving the collet inserted therein along an axis (AX) thereof; a holder containing the collet therein and configured to be movable together with the collet along an axial direction; a nut (N) fitted on the chuck body and containing the holder ; and the holder having a movement allowing mechanism for allowing the holder to move relative to the nut (N) along the axial direction (x) when the nut (N) is moved relative to the chuck body along the axial direction; wherein the holder includes a first holder member contained in the nut (N) and a second holder member contained in the first holder member and containing the collet ; the first holder member and the second holder member are movable relative to each other along the axial direction (X); the first holder member and the second holder member are formed annular about the axis (AX); the movement allowing mechanism includes an engaging protruding portion provided in one of the first holder member and the second holder member along a circumferential direction relative to the axis (AX) and an engaged receding portion provided in the other of the first and second holder members along the circumferential direction and engageable with the engaging protruding portion ; characterized in that the engaging protruding portion is elastically deformable in the radial direction (R); and the engaged receding portion includes a pair of small receding portions provided side by side along the axial direction (X) and holding the engaging protruding portion and a protrusion provided between the small receding portions . <EOS>