Abstract: In a groove-formed body, a recess and protrusions are formed on a resin plate by irradiation with a laser. When forming the recess and the protrusions on the resin plate, the laser is irradiated onto the resin plate plural times. Irradiation of the laser onto the resin plate is thus temporarily paused to cool the resin plate, enabling the portion of the resin plate irradiated by the laser to be suppressed from igniting and enabling a depth dimension of the recess and a height dimension of the protrusions to be made larger.

Abstract: A technique for preventing the extrusion of fused material from between resin parts when the resin parts are laser welded. A case has a resin first case part transmissive to laser light and including a peripheral portion. A resin second case part absorbs laser light joined with the first case part. A light reflector reflective to laser light is formed in the peripheral portion of the first case part. A laser welding portion is formed inward from the light reflector between the first case part and the second case part and located at a region reachable by laser light transmitted through the first case part without being reflected by the light reflector. The laser welding portion is for welding the second case part to the first case part with laser light.