In a spindle apparatus for a machine tool, a spindle is supported on a housing by support-purpose bearing devices, and is rotated by an electric motor, and a tool is attached to a tool attaching portion formed at a distal end of the spindle. A radial magnetic bearing for vibration suppressing purposes which includes a plurality of electromagnets is provided around the tool attaching portion of the spindle. A plurality of radial displacement sensors for detecting a displacement of the tool attaching portion in radial directions are provided around the tool attaching portion. There is provided an electromagnet control unit for controlling the electromagnets of the radial magnetic bearing on the basis of outputs of the radial displacement sensors so as to support the tool attaching portion in a predetermined position.