A vibration welding apparatus and a method for executing vibration welding of three or more work pieces made of a thermoplastic material to make them integral in a sandwich shape, comprises an upper tool means supporting a first work piece so as to apply a lateral motion to it by a vibration means, a lower tool means capable of supporting a plurality of second work pieces to be welded to at least both surfaces of the first work piece, and a means capable of actuating the lower tool means in such a manner as to move the second work pieces vertically by an elevating means so as to align with the first work piece, and move the second work pieces toward the first work piece laterally by a slide actuating means so as to bring them into contact with the first work piece.