Reconditioning is performed such that the curvature of the arcuate surface of the crest on the upper corrugating roll is increased as compared before conditioning. Further, reconditioning is performed such that the curvature of the arcuate surface of the crest on the lower corrugating roll is increased as compared before conditioning. In this step, polishing is performed so as to maintain the maximum diameter of the crest on the upper corrugating roll as much as possible. Thereby, since the length of the inclined surface of the corrugating roll connecting between a crest and a trough of the upper and lower corrugating rolls and is reduced, the rate of the increase in the consumption of corrugated mediums of fluted corrugated mediums for double-faced corrugated cardboard sheets shaped by the upper and lower corrugating rolls and after reconditioning can be reduced.