To suppress occurrence of welds on the downstream side of openings.

While openings 2 are provided in a resin molded body 1, a first recess 3 is provided in the rear of the resin molded body 1 and on the downstream side of the openings 2 in the direction C of flow of injected molten resin, and a pattern part 5 is provided on the downstream side of the recess. A plurality of second recesses 4 constituting the pattern part 5 are formed respectively in the shape of longitudinal grooves in directions intersecting perpendicularly the direction C of flow, and a thin wall part is formed in the resin molded body 1 on the downstream side of the openings 2 by the first recess 3 and the second recesses 4. Although the injected molten resin joins on the downstream side of the openings 2 after it is made to branch by the openings, the flow thereof is disturbed there by the first recess 3 and the pattern part 5 and therefore the resin hardly causes welds 6.