To provide a log cutting device in which the structure of a chipper canter heretofore available is improved, interlocked grains and chipped grains and deficits of a material are controlled and a square material of improved surface quality can be manufactured.

In the constitution of a log cutting device in which a pair of rotating disks 1, 1 provided with knives are disposed facing each other, a log is set between the rotating disks and back plate sections of both faces of the log facing each other are cut by the knives of the rotating disks and the back plate sections are formed into chips, and then the log is revolved by 90° and cut and formed into shapes similarly to manufacture a rectangular lumber as a main product and chips simultaneously, and a pair of circular saws 10, 10 are disposed at the interval narrower than the interval between the rotating disks, and the circular saws are driven by the rotating speed different from that of the rotating disks. As a suitable actual example, driving shafts 3 of rotating disks are formed into the hollow shape, and driving shafts 11 of the circular saws are run through inside of the hollow rotating disks in the concentric shape and rotated relatively.