To reduce the cutting noise and prolong the lifetime of a saw blade by decreasing its chattering when the cutting operation is to be started.

A chatter sensing device 23 equipped with a proximity sensor 65 for sensing the chattering in thickness direction of a saw blade T is installed on a guide member 21 to guide a saw blade T, and a control device 67 for the saw blade T is furnished to increase the cut-in speed by lowering the saw blade speed with the max. cut-in amount per tooth used as the upper limit on the basis of the sensing value of the sensor 65, the saw blade speed, the cut-in speed. This decreases the chatter of the saw blade when the cutting operation is to be started, reduces generation of the cutting noise, and allows prolongation of the lifetime of saw blade.