Main spindle device for machine tool and machine tool

A spindle device of a machine tool, comprising:

• a spindle to which a tool is fitted;
• a bearing for rotatably supporting the spindle;
• a bearing case for holding the bearing;
• a housing in which the spindle, the bearing, and the bearing case are arranged;
• a rigidity switching device supporting the bearing case on the housing and capable of switching support rigidity for supporting the bearing case at a plurality of stages of rigidity including low rigidity and high rigidity higher than the low rigidity;
• and
• a vibration damping device disposed between the housing and the bearing case and actuated when the rigidity switching device supports the bearing case with the low rigidity, wherein
• the vibration damping device includes a friction member disposed in a contact part of the housing and the bearing case,
• the rigidity switching device is formed to move the bearing case along a rotational axis of the spindle in the housing,
• the bearing case includes a tapered part in which a diameter of an outer surface is gradually reduced, and
• the rigidity switching device supports the bearing case with the high rigidity by moving the bearing case to press the tapered part to the housing, and supports the bearing case with the low rigidity by providing the tapered part with a gap.