The subject innovation is increased and the assembly work efficiency by changing to a jet flow of the coolant only replacement of the sleeve is interposed in the space between the case of placing the processing properties and the range other U- drilling tool or cutting tool for a tool holder bore which relates to a tool holder for NC lathes. Thus in constituting of the subject innovation, the inner diameter for the cutting tool 60 or the U- drilling tool 70 and at the same time selective to the holding configuration the tool holder of the NC lathe that selectively formed in the coolant to each tool in accordance with the tool holder 10 is configured to be moved to a predetermined variable range in the coolant supply passage 12, the coolant flow regulating unit to regulate the flow of coolant supplied from the coolant port 15 therein; Wherein provided between the rear end and flow enforcement plate (13) of the coolant flow regulating unit, always the coolant flow downstream side end of the regulating unit of the elastic force is pushed in the forward direction in the state protruding in a length giving an elastic spring 17; But provided between the inner side of each tool 60, 70 and the tool holder 10, when holding the U- drilling tool 70 at the front on both sides are symmetrical to each other as not to interfere with the projecting end of the coolant flow regulating unit the through-holes 21 which are conditions leading to rear flow of the coolant and, when holding a for inner cutting tool (60) to push the coolant flow regulating unit, each intermittent hole 22 leading to the forward flow of the coolant is position formed sleeve (20); It was configured to include.