To solve problems in processing a siding board as a wall material wherein, the siding board is manually cut with a saw generating dust, causing mal-hygienic state for a worker.

The siding board A is placed on a suction table 18 by pressing it to a positioning cylinder 20, and the positioning cylinder 20 is driven to position the longitudinal direction of the siding board A. A ruler vertical cylinder 21 is raised and the extrusion piece 23a of an extrusion cylinder 23 is driven to position the width direction of the siding board A. The suction table 18 is moved toward a head 10 direction, a space is secured between the suction table 18 and a circular saw 11 to prevent the contact of the circular saw 11 with the suction table 18, the head 10 is lowered by a servo motor 13, and cutting parts E, F, G of the siding board A are cut with the circular saw 11, to form a square member C or a tilted member D.