To provide a machining device which is provided with a plurality of rotary units for machining having machining tools such as cutting tools suit able for working on a work, in which a rotary unit can be replaced with another one via installation of the unit to a frame, in which machining is carried out after selecting a rotary unit equipped with a machining tool most suitable for the working on the work, and in which the rotary unit can be replaced at the completion of a prescribed machining in order to carry out the subsequent machining.

A rotary unit 10 for machining, in which a semicircular, first rotary member and a semicircular, second rotary member 27 are connected by a connecting member in an openable/closable manner, can be attached for replacement to a frame 11, in which a first frame member 12 and a second frame member 14 can be opened/closed, centering around a supporting shaft. After installation to the frame 11, the rotary unit 10 for machining is held in a rotatable manner and is rotated. At the same time, the frame 11 is moved along a guide surface of a bed 2, so that the work is machined by a cutting tool 48 attached to the rotary unit 10 for machining.