Light irradiating apparatus and welding method

A welding method using a light irradiating apparatus, wherein

• the light irradiating apparatus includes
• a light source unit including an emission surface and a plurality of point light sources arranged on the emission surface, and
• an optical system that focuses a plurality of light beams emitted from the point light sources into a single light beam and irradiates a target object to be irradiated with the single light beam,
• the single light beam is obtained with a desired light intensity profile according to a combination of positions where the point light sources are arranged and intensity distributions of the light beams emitted from the point light sources,
• the light beams emitted from the point light sources are infrared laser beams, and
• the target object is a resin member, a bonding surface of which is welded by irradiation of the light beam having the desired light intensity profile.