To provide a slitter scorer capable of realizing surely lateral positioning at a low cost.

A trim shooter 30 has a duct 31 and a guide plate 32 for holding a corrugated fiberboard web 2. The plate 32 has openings 33 for sucking trims at both sides. The openings 33 are always disposed at a predetermined positional relation to a trim cutting line TL. Holes 34 are opened at the plate 32 of its upstream side. Photoelectric tubes 40 are respectively arranged in the holes 34 so as to detect the presence or absence of the trim 13 from the hole 34. When either one tube 40 cannot detect the trim, the slitter scorer 3 is moved in a lateral direction B to regulate the positional relation to the web 2 so as to detect the trims 13 by all the tubes 40.