The damping property of a rear rolling bearing (133) is adjusted by controlling a damping force that is applied by damping application means (5, 134) based on, for example, the type of a tool (T). Thus, it is possible to provide the optimum damping properties for various tools that differ in natural vibration, and to suppress the generation of chattering of the various tools. As a result, it is possible to increase the cut amount per unit time to increase the productivity.