To provide a light source device having a small etendue value while enhancing use efficiency of exciting light.

A light source device comprises: a substrate 41; a phosphor layer 45 that is disposed on the substrate 41 and is excited by exciting light so as to emit fluorescent light having a different wavelength from that of the exciting light; a light source 10 emitting the exciting light; a wavelength selective mirror 60 that is disposed opposite to the phosphor layer 45 on an emitting side of the fluorescent light from the phosphor layer 45 and transmits light corresponding to a wavelength band of the fluorescent light while reflecting light corresponding to a peak wavelength of the exciting light toward the phosphor layer 45; and a pickup lens 50 disposed between the wavelength selective mirror 60 and the phosphor layer 45.