To make it possible to compose and output light rays from a main light source effectively.

The light source device comprises: the main light source for emitting white light and an auxiliary light source for emitting monochrome light; a dichroic mirror 8 that reflects a luminous flux of a predetermined wavelength area in which a quantity of illuminating light from the main light source is smaller than that from the auxiliary light source, and transmits light of wavelength areas other than the predetermined one; a condenser lens 10 by which, of the illuminating light from the main light source, the illuminating light reflected by the dichroic mirror 8 is condensed; an optical fiber 11 by which light condensed by the condenser lens 10 is guided to the place where this condensed light is combined with the illuminating light emitted by the auxiliary light source; and a collimating lens 12 by which light emitted from an optical fiber 11 is converted into a substantially parallel luminous flux. Of the illuminating light emitted by the main light source, light reflected by the dichroic mirror 8 is effectively used.