PURPOSE: To automatize and unman a soft jaw forming, by feeding a ring for soft jaw forming to a soft jaw by a ring holder in case of the soft jaw processing, and feeding the ring without interposing hands in case of the soft jaw forming.

CONSTITUTION: A ring holder 12 stored in a storage means is installed to a cutting tool post 7 in the case of the work of a soft jaw 6 installed to a work main spindle 21 via a chuck 22, a ring 11 installed to the ring holder 12 placed on the cutting tool post 7 is held at the ring fitted position of the soft jaw 6 in a release state, the ring holder 12 is pulled out of the ring 11 in that state, and it is composed so as to perform the work of the soft jaw 6. The need for feeding the ring 11 by a worker whenever the soft jaw forming is performed is eliminated therefore, the automatization/unmanning of the soft jaw forming becomes possible. Also the ring holder 12 forms the installation part of a tapered shank, pullstud, etc., on a main body 13, and it is composed by providing a ring holding part 32 which holds the ring 11 freely detachably on the main body 13.