Slitter apparatus with a compensating device for slitter blades thereof to provide a stable or proper operation for cutting a corrugated cardboard sheet. The slitter comprises positioning sensors (50) for detecting the vertical position of each of the disk-shaped slitter blades (40), and an optical sensor (58) having an optical axis (60) generally disposed in a parallel relationship with respect to the corrugated cardboard sheet. The disk-shaped slitter blades of the slitter heads (20-24) are moved one by one toward the optical axis (60) of the optical sensor (58) in such a way that the respective circumferential cutting edges of the disk-shaped slitter blades (40) interrupt the optical axis (60) of the optical sensor (58), whereby the radius of each of the disk-shaped slitter blades (40) is measured and the depth of engagement between the circumferential cutting edges of the disk-shaped slitter blades (40) and slitter pads is compensated accordingly.