PURPOSE: To enable a rotary cutter to be fixed at any desired position in the captioned slitter for cutting through to divide metal belt, by providing a cutter fixing device in which a rotary cutter is mounted on the outer face of an outer taper sleeve and an oil film is hydraulically formed on the surface and back face of an inner taper sleeve adapted to be pressed into or drawn out.

CONSTITUTION: High-pressure oil is fed from the end (a) of the blade axis such that the inner and outer faces of an inner taper sleeve 14 is swelled by the high pressure oil and an oil film is formed thereon. The inner taper sleeve is pressed into by means of an outer nut 15 to increase its outer diameter. In case of decreasing the diameter, the inner taper sleeve is drawn out with an inner nut 16. This constitution allows a rotary cutter to be fixed at any desired position.