A beam splitter comprising: a light incident surface; a beam splitting surface which is inclined with respect to the light incident surface, wherein the beam splitting surface is oriented to reflect light having a first wavelength, incident thereon from the light incident surface, and to transmit light having a second wavelength, incident thereon from the light incident surface, wherein the second wavelength is different from the first wavelength; a first light exit surface which is oriented such that the light having the first wavelength that is reflected from the beam splitting surface exits the beam splitter through the first light exit surface; a first reflective surface which is oriented to reflect the light having the second wavelength that has been transmitted through the beam splitting surface; a second reflective surface which is oriented to reflect the light having the second wavelength that has been reflected from the first reflective surface; and a second light exit surface which is oriented such that the light having the second wavelength that has been reflected from the second reflective surface exits the beam splitter through the second light exit surface; and further comprising a first reflective member disposed on the first reflective surface, and a second reflective member disposed on the second reflective surface and wherein a reflection-type modulator which modulates and reflects the light having the second wavelength is disposed on one of the first reflective member and the second reflective member, and the other one of the first reflective member and the second reflective member comprises a reflective mirror. a light incident surface; a beam splitting surface which is inclined with respect to the light incident surface, wherein the beam splitting surface is oriented to reflect light having a first wavelength, incident thereon from the light incident surface, and to transmit light having a second wavelength, incident thereon from the light incident surface, wherein the second wavelength is different from the first wavelength; a first light exit surface which is oriented such that the light having the first wavelength that is reflected from the beam splitting surface exits the beam splitter through the first light exit surface; a first reflective surface which is oriented to reflect the light having the second wavelength that has been transmitted through the beam splitting surface; a second reflective surface which is oriented to reflect the light having the second wavelength that has been reflected from the first reflective surface; and a second light exit surface which is oriented such that the light having the second wavelength that has been reflected from the second reflective surface exits the beam splitter through the second light exit surface; and further comprising a first reflective member disposed on the first reflective surface, and a second reflective member disposed on the second reflective surface and wherein a reflection-type modulator which modulates and reflects the light having the second wavelength is disposed on one of the first reflective member and the second reflective member, and the other one of the first reflective member and the second reflective member comprises a reflective mirror.