A lamp (1) having a semiconductor light-emitting element (12) for functioning as a light source, and a circuit unit (40) for causing the semiconductor light-emitting element (12) to emit light, are housed in an outer package (2) that contains a cylindrical outer tube (30) and a socket (60), wherein: the semiconductor light-emitting element (12) is positioned so as to face a principal emission direction opposite the direction of the socket (60), and nearer the socket (60) than the center region in the direction of the tube axis of the outer tube (30); at least part of the circuit unit (40) is positioned on the opposite side of the center region from the semiconductor light-emitting element (12); a light-guiding member (50) for guiding light in the tube-axis direction is positioned between at least part of the circuit unit (40) and the semiconductor light-emitting element (12); and the section of the light-guiding member (50) corresponding to the center region has been diffusion-treated.
