The present invention relates to an optical waveguide-type optical multiplexer, an optical waveguide-type multiplexing light source optical device, and an image projecting device, and attenuates the intensity of a light beam from a light source to a desired value without installing an additional light-attenuating element. Among a plurality of light output-side optical waveguides that output light that has been distributed and multiplexed in an optical multiplexer portion, when a plurality of light sources are driven, one light output-side optical waveguide other than the light output-side optical waveguides in which maximum output optical powers are obtained respectively at all wavelengths is used as a light-outputting optical waveguide.
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