Optical semiconductor element mounting package and optical semiconductor device using the same

An optical semiconductor element mounting package as well as an optical semiconductor device using the package are provided. The optical semiconductor element mounting package has a recessed part that serves as an optical semiconductor element mounting region. The package includes a resin molding and at least a pair of positive and negative lead electrodes. The resin molding is composed of a thermosetting light-reflecting resin composition, which forms at least the side faces of the recessed part. The lead electrodes are disposed opposite to each other so as to form part of the bottom face of the recessed part, and there is no gap at a joint face between the resin molding and the lead electrodes.