Abstract: There is provided a light source device which can output simultaneously a light in the C band and a light in the L band. The light source device includes a reflection end which reflects an input light, a first EDF which is connected at one end to the reflection end, and outputs a first spontaneously emitted light (C band) by means of a first excitation light input from the other end, a second EDF which is connected at one end to the other end of the first EDF, and outputs a second spontaneously emitted light (C band) by means of a second excitation light input from the other end, where the second EDF converts the first spontaneously emitted light (C band) input from the one end to a longer wavelength light (L band), and outputs the longer wavelength light. From the other end of the second EDF are output simultaneously the second spontaneously emitted light (C band) and the longer wavelength light (L band).