Abstract: Disclosed is a sheet material slotting device provided with an upper slotter shaft and a lower slotter shaft, in a vertical relationship, which rotate in opposite directions to each other in synchronization with the speed of feeding the sheet material; and an upper slotting knife disposed relative to a ring attached to the upper slotter shaft and also a pair of lower slotting knives disposed relative to a ring attached to the lower slotting shaft, with a predetermined space therebetween, in the axial direction and having a constitution in which slotting of a sheet material is carried out under cooperation of the upper slotting knife with the lower slotting knives characterized in that said slotting device comprises:an eccentric member fitted to the upper slotter shaft having an axis deviated from the axis of said shaft;a holder pivotally fitted with play around the outer periphery of this eccentric member and having the upper slotting knife fixed thereon so that the edge of said knife may be extended outwardl