To enable a plurality of machining work without changing a holder by enabling a slide part to be moved between the symmetrical sections with respect to an axis extending along the face plate diameter direction, and mounting a holder for holding two different blade tools back to back in the face plate diameter direction on a tool box in the direction in which the blade tools extend in the moving direction of the slide part.

A slide part 21 is moved in the plus side direction of a U shaft, and a blade tool 23 is positioned in the distance L1 in relation to the center shaft M of a face plate 7 and machined according to characteristics of the blade tool 23. The slide part 21 is faced to the axis side of the face plate 7, a holder 9 is moved from the section t1 to the other section t2 over the axis M of the face plate 7, the other blade tool 24 is positioned in the distance L2 in the section t2 and machined according to characteristics of the blade tool 24. Therefore, two kinds of machining can be performed without changing a holder 22.