To provide a positioning device for a cutting edge of a slitter, which fixes a cutting edge holder to an intended position in the width direction of a sheet-shaped object and fixing the cutting edge holder, prevents change in the posture of the cutting edge holder and the cutting edge during fixation of the cutting edge holder, and highly accurately positions the cutting edge.

The cutting edge holder 16 having the cutting edge is held on a slide guide 14 so as to be movable by a pair of slide blocks 22, and a push pin 33 for pushing the cutting edge holder 16 is provided on a positioning block 31 moved in parallel with the slide guide 14. By the movement of the positioning block 31, the cutting edge holder 16 is pushed to the intended position. In the cutting edge holder 16, a lock member 23 and a lock member driving means 24 for driving the lock member 23 are provided in the middle of the pair of the slide blocks 22. By pushing the lock member 23 on the slide guide 14 in the middle of the pair of the slide blocks 22, the cutting edge holder 16 is fixed to the slide guide 14 without changing the posture of the cutting edge holder 16.