A surface treatment is carried out on a surface of an inner circumferential die 53 among dies for forming a distal end cover of a capsule endoscope by irradiating ion beams from an ion source 55 of an ion implanter so that fine and random irregularities are generated on the surface of the inner circumferential die 53 to the extent that the surface of the inner circumferential die 53 is slightly roughened. Next, by forming the distal end cover that is a molded product by injection molding while combining this inner circumferential die 53 with other dies, a molding performance for molding the distal end cover is improved without hampering an imaging performance of the capsule endoscope.
