Spindle head for machine tool

A spindle head for a machine tool, the spindle head including a main shaft (9) that rotatably supports a spindle (10) to which a tool is mounted;

• a pair of support shafts (58, 59) including coaxial axial lines which intersect the main shaft (9), the pair of support shafts (58, 59) being provided on respective sides of the main shaft (9) and being secured to the main shaft;
• a frame (4) that rotatably supports the pair of support shafts (9);
• and a rotation driving device (56) for at least one of the pair of support shafts (58, 59), in which the spindle (10) is rotated around the axial lines of the support shafts (9) by the rotation driving device (56),
• wherein the spindle head comprises a clamping device (57) and connection sections, the clamping device (57) being disposed around the axial line of the support shaft (59) and including a push member (19, 20) for maintaining a rotation position of the spindle (10) by directly or indirectly acting upon the support shaft (59), the connection sections being provided coaxially with the axial line of the support shaft (59) from an acting position of the push member (19, 20) to the main shaft (9) at the axial line of the support shaft (59), the connection sections being fastened to each other by a bolt group (311), the connection sections being connected to each other so as to be prevented from rotating relative to each other by friction force resulting from the fastening, wherein rotation prevention torque based on the friction force is a value greater than torque applied to the connection sections during processing and smaller than torque applied to the connection sections when an external force that causes the spindle (10) to deform beyond a permissible range during operation of the clamping device (57) is applied to the spindle (10).