PURPOSE: To reduce vibration and noise by reducing the exciting force acting on respective rolls such as upper and lower stage rolls, a pressure roll or the like.

CONSTITUTION: In the single facer of the corrugating machine producing a single-faced corrugated cardboard sheet, the steps of upper and lower stage rolls 1,2 are divided into a plurality of zones in the lateral direction of the rolls and the phases of the ridges of the steps at every zones are shifted mutually to reduce the exciting force applied to the upper and lower stage rolls 1,2 and a pressure roll 3. A slitter knife 7 for dividing and cutting core paper 4 in the lateral direction thereof in matching relation to the zones of the stage rollers is provided on the upstream side of the upper stage roll 1.