A tool made of a cubic boron nitride sintered body which has a long life in a stable manner in any application of cutting and plastic working is provided. The tool made of the cubic boron nitride sintered body according to the present invention includes a cubic boron nitride sintered body at least at a tool working point and it is characterized by satisfying an Equation (I) and any one of an Equation (II) and an Equation (III)
where a ratio of cubic boron nitride contained in the cubic boron nitride sintered body is denoted as X volume % and thermal conductivity of the cubic boron nitride sintered body is denoted as Y (W/m—�K).
