Abstract: The present invention relates to a spindle unit of a machine tool in which tools changing is available and especially relates to a spindle unit by which a tool in a tool holder can be quickly and safely clamped and unclamped. This spindle unit is characterized in that an operating hole along with the centerline axis of a rotary spindle is provided therein for fixing (or clamping) a tool, a draw bar furnished with a cylindrical body along with the inner circumferential face of the operating hole is provided therein, the lower portion of the cylindrical body is formed on the inclination face of a wedge body, and a tool is clamped by guiding a ball by which the pull stud of a tool holder is engaged, along with the inclination of the inclination face of the wedge body, that is, by movement of the ball toward the center of the spindle, and is unclamped by the reverse movement of the ball.