PURPOSE: To reduce cutting noise by detecting the variation in the cutting length from the variation in hydraulic force acting on the elevating hydraulic cylinder of a saw frame, and reducing the running speed of a band saw at a cutting place where the cutting length is small.

CONSTITUTION: Each displacement end of the contact operating pressure of a pressure gauge with a contact point (not shown in the figure) and the pulley 18a of a speed change gear 18 set, before a cutting operation is started. To set the contact operating pressure, when an H-type angle steel is to be cut, for example, setting is made in such a way that a solenoid (not shown in the figure) is excited by means of variation in pressure caused by the arrival of the cutting place at a wave part. When a flange part is being in the initial stage of starting cut, the cutting length is small and the band saw 17 is run at a low speed, thereby reducing noise.