PURPOSE: To achieve recessing of the surface of the bore diameter, by mounting a detachable head cap on the tip of the head main body at an arbitrary angle, and further by fitting a rotatable drill chuck on the head main body at the right angle to the head spindle via bevel gear.

CONSTITUTION: Eyebolts E for hanging are fitted into tapped holes 10, 10' of the head main body. Then the head was hanged by wire, and carried to a boring machine B to be connected to the spindle via an end flange 2. A gear 4 of a head spindle 3 is connected to a gear G of a boring bar of the boring machine B. As the boring bar of the boring machine B rotates, a drill chuck 9 is rotated by power transmission from bevel gears 8, 8' of the head spindle 3 which are mounted and supported by a head cap 7. Thus, the inside of the hole of a workpiece W can be machined by the end mill, drill or reamer mounted on the drill chuck 7.