To improve cutting conditions and working efficiency by injecting a cutting oil automatically on an optimum position.

This device is provided with a guide arm 27 on fixed side and a guide arm 31 on moving side to guide a band saw blade 21 in a saw blade housing, a magic hand (registered trademark) 49 as an expansion device 35 which is capable of expansion and contraction between the guide arm 27 on fixed side and the guide arm 31 on moving side, and an injection nozzle 39 equipped with a cutting oil supply device 37 to supply a cutting oil in nearly a center of the expanding direction of the magic hand 49. Hence, cutting oil can be injected automatically on an optimum position and cutting conditions and working efficiency can be improved.