To apply direct printing to a microflute single-faced corrugated cardboard of which the height of a corrugation among molded corrugations is 1 mm or below and smoothly supplying and transferring a sheet on a printing machine while preventing registering shift at multicolor printing.

Liner raw paper is pasted on one side of corrugated core raw paper and the sheet obtained after pasting is cut to form the single-faced corrugated cardboard sheet with a corrugation height of 1.0 mm or below and the number of corrugations per 30 cm of 90 or above. An appropriate pressure means is used prior to printing the whole surface of the single-faced corrugated cardboard to pass, for example, the single-faced corrugated cardboard sheet through the gap between two upper and lower pressure rolls 10a, 10b to compress the sheet in its thickness direction.