A chattering vibration inhibiting mechanism capable of inhibiting chattering vibration of a machine tool without increasing weight nor requiring a time-consuming adjustment work is provided. A box-shaped package body 21 attached to a spindle head 6, a supporting member 22 disposed to bridge between front and rear walls 21a, 21b in the box-shaped package body 21, and a damper 23 composed of an elastic member 27 and a weight 26 supported by the supporting member 22 are provided.