Main spindle device of machine tool

A main spindle device for a machine tool, including:

• a main spindle that holds a tool and that is driven for rotation;
• a plurality of bearings that rotatably support the main spindle;
• load deriving means that derives loads that respectively act on the bearings from a variation in a state of the main spindle resulting from machining using the tool;
• contact pressure analyzing means that analyzes raceway surface contact pressures of the respective bearings on the basis of the loads that respectively act on the bearings and that are derived by the load deriving means;
• and
• control instruction means that compares the raceway surface contact pressures of the respective bearings, analyzed by the contact pressure analyzing means, with preset thresholds of the raceway surface contact pressures of the respective bearings, and, when at least one of the raceway surface contact pressures exceeds a corresponding one of the thresholds of the raceway surface contact pressures, issues instructions to change a machining condition or issues instructions to stop the main spindle.