PURPOSE: To make V-grooves crossing perpendicularly each other with high accuracy without changing the direction of the board in the way by rotating Z-axis holders arranged while facing with an X-axis sliding body such that the rotary axes of respective disc cutters direct in X-axis direction and Y-axis direction.

CONSTITUTION: Upon reception of a command for machining a V-groove 32a in X-direction, Z-axis rotary units 18, 19 operate in one way to rotate the rotary axes of respective disc cutters 16, 17 in the direction perpendicular to an X-axis rail 1, then an X-axis drive unit 5 operates to move respective disc cutters 16, 17 in X-direction. Upon reception of a command for machining a V-groove 32b in Y-direction, the Z-axis rotary units 18, 19 operate in the other way to rotate the rotary axes of the disc cutters 16, 17 in parallel with the X-axis rail 1 then a Y-axis drive unit 27 operates to move a board material 31 in Y-direction.