To reduce in size electrodes of an induction heater without warpage by minimizing a change in a water content of a liner and to accelerate a line speed by effectively gelatinizing a paste in a short time.

A double faced corrugated fiberboard 5 is obtained by the steps of corrugating a rear liner 2 heated to 50 to 100°C, closely contacting the liner 1 with a pasted corrugating medium 1, induction heating the liner 1 and the medium 1 to adhere the liner 1 to the medium 1 to a single faced corrugated fiberboard 4, and then adhering a front liner 3 to the pasted fiberboard 4. Water contents of both the front and the rear liners in manufacturing steps are not almost changed by heating it in the temperature range before the front and the rear liners are induction heated and adhered.