Abstract: In a double facer in which a one-sided corrugated board and a liner sheet which are web-like and which are superposed with each other are glued to each other while they travels on a heating plate so as to produce a corrugated board, the heating plate has a thin wall thickness so as to enhance the efficiency of heat transfer to a paper sheet which travels on the upper surface of the heating plate, and the heating plate 20 is provided at the lower surface thereof with a heat radiation means (having the configuration that reinforcing ribs 22 are formed at the lower surface of the heating plate in a direction orthogonal to the direction of travel of a paper sheet, having their height which are successively decreased, or several steam through-holes 51 are formed in the heating plate, and are adapted to be fed therein with saturated steam whose pressure or temperature is successively lowered) in order to decrease a temperature difference between the upper surface and the lower surface of the heating plate so as to