In a resin joined body including at least one member made of a resin material that forms a first resin layer and a second resin layer, the at least one of the first and second resin layers having the rear side from which the laser beam has been irradiated has an absorption constant of 50 to 5000 m−1 for the wavelength of the laser beam, and the fuse bonded portion is formed to have a relationship of X>Y, wherein a light transmittance of light passing from the first resin layer to the second resin layer via the fused portion is designated as X(%), and a light transmittance of light passing continuously from the first resin layer to the second resin layer via a portion other than the fused portion is designated as Y(%).