PURPOSE: To cut a flat and wide large steel member efficiently and accurately by cutting the material to be worked and secured on a table by means of a belt saw edge travelling longitudinally.

CONSTITUTION: A table for mounting a material to be worked G is constructed with an outer table 14 at the outside of the cutting position and an intermediate table 15 at the inside of the cutting position. A clamping device 20 for securing said material G is provided on the outer table 14 to secure said material G. In order to cut the material by means of said longitudinal saw board, the longitudinal frame 3 is returned to the reset position then the belt saw edge 10 is travelled toward material G then the frame 3 is fed from the front to the rear.