PURPOSE: To execute accurate and easy cutting of a groove on a decorative sheet and easily giving the stereoscopic view by marking at the position where the groove is to be formed, with paint containing material able to be read and transmitting the read data from a reading equipment to a groove cutting machine.

CONSTITUTION: Marking is executed with crayon or similar material containing much metal ingredients along the wood trimming joint parts of single boards 2 on the surface of a decorative board 1. The decorative board 2 is fed beneath a ultra-sonic sensor device and read for the part marked with the crayon by said device. The read data is stored in a computer and transmitted to a multi- axis NC router to cut the marked part only of 2mm in width and 1mm in depth, for example, to form a horizontal groove 3. Finally, the vertical groove 6 continuing from end to end of the decorative board 1 is cut along the seam in the direction of the width of the single boards 2 on the surface of the decorative board, whereby finishing a stereoscopic decorative board with each of the single boards 2 surrounded by both the horizontal grooves 3 and the vertical grooves 6.