A method for manufacturing a resin molding can be provided that uses a laser beam. The method can include providing the resin molding including welded portions that can impart high level of adhesion, have excellent appearance and provide very strong bonding strength. The method can also include arranging and pressing a weld region of a light-absorbing resin member and corresponding weld region of a light-transmitting resin member that are opposed to each other, and setting a plurality of irradiation areas in the extending direction of the welded regions. The method can also include arranging a plurality of laser irradiation scanning heads corresponding to the irradiation areas. Here, the irradiation areas can include a single irradiation area which the corresponding scanning head can irradiate with the laser beam and a composite irradiation area which the adjacent scanning heads can irradiate with respective laser beams. The method can further include causing the plurality of laser beams emitted from the scanning heads to repeatedly scan the single irradiation area along a first trajectory in the extending direction of the single irradiation area and part of both the single irradiation area and the composite irradiation area along a second trajectory in the extending direction, so that the entire welded regions are heated and fused to weld the light-transmitting resin member and the light-absorbing resin member.