PURPOSE: To ensure the improvement of cutting efficiency without any excessive load on a band saw blade by detecting cutting resistance in sawing a workpiece and controlling an actual cutting speed on the basis of the predetermined cutting resistance, cutting speed and cutting speed reduction ratio.

CONSTITUTION: An endless type band saw blade T turning driven by a servo motor 17 cuts a workpiece W in such a way as to be pressed to the workpiece W via a blade guide through the application of hydraulic pressure to a lift cylinder 37 via a selector valve 47. In this case, a rear component as one of component forces is detected with the load sensor 33 of a load detecting device 23. Also, the turning of a band saw blade housing or the cutting speed of the blade T through the adjustment of the quantity of oil discharged from the lift cylinder 37 via a flowrate adjusting valve 61 is measured with a rotary encoder 67. Furthermore, a control device regulates an actual cutting speed on the basis of a detected cutting resistance and the predetermined cutting resistance, cutting speed and cutting speed reduction ratio. According to the aforesaid construction, cutting efficiency can be improved without any excessive load on the band saw blade.