PURPOSE: To provide a rotary tool holder in which a rotary body for fitting a tool or an intermediate rotary body for supporting this rotary body via a bearing is retained by an unrotary retaining body via a bearing, in which infiltration of chips and working fluid is completely prevented, early stage wearing of the bearing is not caused, durability is excellent, and which is suitable for high speed rotary machining.

CONSTITUTION: An intermediate rotary body 1 for supporting via a bearing 3a a tool fitting rotary body 2 whose one end side is adopted as a tool fitting part 2a is rotatably retained by an unrotary retaining body 4 via a bearing 3c, and air supply passages 11, 14a-14c, 16 are provided for introducing air into an inner space 15 of a fitting part for the bearings 3a, 3c. The air introduced into the inner space 15 is blown out to the outside through gaps g1-g3 of relatively rotating parts.