According to one example, an optical element assembly includes a transparent rod, a mirror and a light emitting element. The rod transmits light of first wavelength region made incident on a first end of the rod and emits the light of the first wavelength region from a second end of the rod. The rod absorbs light of a second wavelength region falling out of the first wavelength region. The mirror is disposed on a side of the first end. The mirror transmits one of the light of the first and second wavelength regions, reflects the other. The light of the first and second wavelength regions are made incident on the first end of the rod. The light emitting element emits light of the second wavelength region made incident on the first end of the rod through the mirror.