A valve body of an intake controlling valve, which is selectively opened and closed to communicate and interrupt communications between chambers which are divided by a partition wall in a resin surge tank, may be used for internal combustion engines. A variable intake device for an internal combustion engine is manufactured such that the valve unit is integrally assembled to a resin surge tank body by installing the valve unit into an opening of an outer wall of the resin surge tank and an opening of the partition wall formed at the partition wall and fixing the valve unit. Between the frame and the opening of the partition wall, and the valve unit and the opening of the outer wall are integrally fixed at their contact portions through adhesion with an adhesive or by welding.