To provide a tool holder clamp unit for use in a machine tool, easily removable from the front of a main spindle.

A clamp mechanism 25 for clamping a pull stud part 212 formed in a taper shank part 211 of a tool holder 21 is stored in a cylindrical case 23 of this tool holder clamp unit 22. A drawing bar 36 connected to a slider 26 to perform an opening/closing operation of a clamp member 27 of the clamp mechanism 25 is projected to the outside from a rear end part of a cylindrical case 31. A belleville spring 43 for always energizing the bar 36 in a rear clamping direction is provided on an outer peripheral surface of the drawing bar 36. The clamp unit 22 is mounted to be removable from the front of the main spindle in a through hole of the main spindle. A mechanism for preventing relative rotation is provided among junction end faces of the cylindrical cases 23 and 31, a storing hole 314 of the cylindrical case 31, and a second engagement part 363 of the drawing bar 36.