PURPOSE: To provide a cutter in which a processing size can automatically be set in response to a change in a thickness of a decorative plywood for forming a columnar body wound on a core material.

CONSTITUTION: A ruler 10 is provided at an edge side of a roller conveyor 5 at one side along a feeding direction, and milling cutters C1-C6 having knives of V shape as a base are arranged corresponding to grooves to be formed. Cutting positions of the cutters C1-C6 are calculated based on a thickness of a plate material M measured by a thickness meter 50 near an inlet of the conveyor, an outer size of a previously input column and a thickness of a mounting film sheet, and stored in a buffer memory. When sensors P1-P6 sense passage of an end of the material, a servo motor is started to move the cutters C1-C6 to cutting positions stored in the memory.