To make joining surfaces coincide surely with each other and to enable precision butt end treatment even in butt end processing in which the inner wall surfaces of a V-groove are combined together to join the end part to the butt end.

A plate-shaped cutter 15 in which blade parts are formed on the peripheral fringe of a surface which is rotated by a rotary shaft and crosses at right angles with the rotary shaft is installed to protrude from the surface of a head 13. A sliding table 19 which slides perpendicularly to the rotary shaft is installed on the surface of the head 13. A positioning means 25 which holds an extrusion molding material 26 to make the extrusion direction parallel with the rotary shaft is installed on the table 19. The cross-sectional shape in the radius direction of the blade parts of the cutter 15 is formed in the same shape with a V-groove.