In a lens device, plastic lenses having circular outer periphery are placed in a plastic lens-barrel having an octagonal or more complex polygonal inner surface in such a way that the outer peripheral surfaces of the lenses are press contacted to the inner surface of the polygonal shape. This lens device has press contact portions that are pressed by the lens outer peripheral surface and the lens-barrel inner surface in the vicinity and in both sides of gate traces where optical axis displacement is large so as to suppress the displacement of the gate trace by the press contact portions.