To hold the amount of bleeding of formaldehyde below a specific value and prevent the adverse effect of an antimildew agent upon a human body from occurring and also prevent the harmful substances such as the chlorine of an organic antimildew agent and a chemical combustion product of a halogen compound from being generated by adding an inorganic antimildew agent to a formalin adhesive.

A silver a tifungus agent such as zeolite-silver, ceramic-silver, zirconium phosphate-silver or calcium phosphate-silver, or an inorganic antifungus agent of copper or zinc series as inorganic antifungus agent is added to a formalin additive as an amino resin aqueous adhesive such as urea resin, urea-melamine cocondensation resin, melamine resin or urea-phenol cocondensation resin, and these components are uniformly dispersed and this dispersion is used. Consequently the amount of bleeding of formaldehyde is considerably lessened to the level of 1.5 mg/l, or less, so that the adverse effect of formaldehyde upon the human body is diminished. Further the wooden board is made more effectively resistant to mildews by the action of an inorganic antimildew agent.