PURPOSE: To restrain the exudation of resin during the main hardening period by high frequency and thus raise the productivity by performing a pre-drying process to the woody materials infiltrated with resin.

CONSTITUTION: Spacers 4 are disposed between woody materials 1 such as veneer and they are laminated in the form of a multistage and thereafter resin infiltration is conducted thereinto by a resin infiltration device 3 and then the solvent is pre-dried in a pre-drying process (a). The pre-drying is carried out for 0.5 - 3 days in the case of wind drying and for 2 - 24 hours in the case of air heat drying in the form of being disposed by spacers 4. And, in the form of removing the spacers 4, they are subjected to decompression in a drying process (b) and pressed by a press P and finally main drying is executed by high frequency heating. In this way, the exudation of resin is restrained during the main hardening period and the use of a film 2 is made unnecessary during the high frequency drying period, with the result that the productivity can be improved thereby.