PURPOSE: To prevent the occurrence of a strain at the shearing side of a band saw, by constituting and setting up a guide plate, being somewhat smaller in thickness than that of maximum one in the band saw so as to be flush with the shearing side band saw as well as to come into contact with the band saw backside part, between guide arms.

CONSTITUTION: A beltlike guide plate 16 being rather smaller in thickness than that of maximum one in a band saw 12 is locked to space between guide arms 14a and 14a with setting blocks 20 and 21, a bolt 29 and so on, while the guide plate 16 is adjusted in height by adjusting bolts 30 and 31, and then a guide piece 34 made of a cemented carbide or the like installed in the guide plate 16 is made so as to properly come into contact with a back part 12b of the band saw 12. Doing like this, the guide piece 34 is made contact with the back part 12b of the band saw 12 whereby a strain in the band saw 12 so that a strain in the band saw can be minimized.