PURPOSE: To enable the stabilized slit of a thick material by adjusting the bend quantity of the steel belt of between two rotating edges deciding the slitting width of the steel belt, in the case of slitting the steel belt by the slitter that a circular cutter is set to a pair of the upper and lower cutter shafts.

CONSTITUTION: In the case of slitting a thick steel body 7 by using a slitter consisting of a pair of the the upper and lower cutter shafts on whose sleeve face plural circular cutters 5, 6 are fitted, the force (f) in the reverse direction to a side part force F acts on a lower circular cutter 6 by the edge bent of a steel belt 7. In order to slit a thick steel belt 7 stably, the strength of a bending force (f) can be adjusted by adjusting the bent quantity of the steel belt 7. Namely, the steel belt 7 can be slitted without moving the set position of the lower circular cutter 6, by taking such a bending force (f) as to balance with the side part force F. As for the means giving the bent quantity to the steel belt 7, there are the method of fitting the rubber ring in the specific diameter between the lower sleeves with its halving and so on.