A light source device according to the present invention includes: a light source section; a light guide member provided at a position where the light guide member receives light emitted from the light source section, the light guide member having a tapered shape in which the light guide member gradually increases in width from its incident surface toward its emission surface, and an optical filter provided at a position where the optical filter receives light emitted from the light guide member, the optical filter reducing a spectrum having a predetermined waveband from the light. This makes it possible to provide a light source device which can control a radiation angle of light and which is downsized, and a pseudo-sunlight irradiation device including the light source device.