To provide a method and an apparatus for manufacture of a building material and a lumber molded product for using, as raw materials, lumber such as domestic lumber, a pine, a Japan cedar, thinnings or the like which are little in deformation or abrasion though used for a long period of time by impregnating the lumber with a thermosetting resin to contribute to reuse of the lumber of demolition wooden house and prevention of global warming.

A reduced pressure cooking process for diffusing a resin in a lumber 12 by reduced pressure cooking the lumber 12 in a cooking tank 14; an impregnation process for vacuum pressure impregnating the lumber 12 passed through the reduced pressure cooking process; and a molding for carrying out plastic compression modification working of the lumber 12 passing through the impregnation process by heating in a resin-heating layer 57 under a state of being equipped to a compression embossing molder 61 to further carry out thermosetting of the impregnated thermosetting resin 27 are provided.