A single facer for manufacturing single-faced corrugated board having a first corrugating roll and a second corrugating roll meshing with the first corrugating roll to form a nip for receiving a sheet medium to corrugate the same, the second corrugating roll being provided with radial conduits extending toward its periphery through which suction is applied for attracting and holding the corrugated medium onto the peripheral surface thereof. The outer ends of the conduits terminate in the bottoms of axially spaced circumferential grooves formed around the periphery of the second corrugating roll. Finger-like plates engage within the circumferential grooves to seal at least some of the conduits disposed in the portion of the second corrugating roll which is not lapped by the corrugated medium. The apparatus further includes an applicator for applying adhesive to the peaks of the flutes of the corrugated medium and a pressure roll for pressing a sheet linerboard against the corrugated medium after the adhesive has been applied to bond the linerboard to the corrugated medium.