Abstract: A quick-change holder for a machine tool wherein a nut holding a tool can be attached and detached by a single action. In the quick-change holder of the type, in which the nut charged with the tool can be attached to and detached from a holder body by the radial movements of a plurality of balls which are so loosely fitted in a plurality of radial through-holes formed in the holder body as to be made movable in the radial direction, according to the present invention, the aforementioned holder body is formed with an outwardly diverging conical inner circumference in which a spring having free wire ends with a gap therebetween so as to be compressible radially inwardly is fitted under radially inward compression in an inscribed relationship therewith, and the aforementioned spring is brought into abutment engagement with the balls, when the nut is not inserted, thereby to push the balls outwardly in the radial direction.