An optical sensor comprising: an emitting system including at least one light emitting device (LM) configured to emit light onto an object; and a detecting system (DM) configured to detect the light which has been emitted by the emitting system and which has propagated through the object, wherein the light emitting device (LM) is capable of emitting a plurality of light beams with different wavelengths onto substantially the same position of the object, wherein the light emitting device (LM) includes i) a plurality of light sources which individually emit respective light beams with different wavelengths; ii) a plurality of individual optical elements arranged on optical paths of the light beams with different wavelengths of the plurality of light sources; iii) and a common optical element which is arranged in common on the optical paths of the light beams with different wavelengths via the plurality of the individual optical elements, wherein the optical paths of the plurality of the light beams with different wavelengths via the common optical element are substantially the same, wherein each of the plurality of the light sources includes a plurality of light emitting units arranged in an array manner, wherein position relationships between the plurality of the light emitting units and an optical axis of the corresponding individual optical elements are different between the plurality of light sources, wherein each light source is a surface emitting laser array, and wherein optical axes of the emitted light beams of the light emitting units with different wavelengths are parallel to each other. an emitting system including at least one light emitting device (LM) configured to emit light onto an object; and a detecting system (DM) configured to detect the light which has been emitted by the emitting system and which has propagated through the object, wherein the light emitting device (LM) is capable of emitting a plurality of light beams with different wavelengths onto substantially the same position of the object, wherein the light emitting device (LM) includes i) a plurality of light sources which individually emit respective light beams with different wavelengths; ii) a plurality of individual optical elements arranged on optical paths of the light beams with different wavelengths of the plurality of light sources; iii) and a common optical element which is arranged in common on the optical paths of the light beams with different wavelengths via the plurality of the individual optical elements, wherein the optical paths of the plurality of the light beams with different wavelengths via the common optical element are substantially the same, wherein each of the plurality of the light sources includes a plurality of light emitting units arranged in an array manner, wherein position relationships between the plurality of the light emitting units and an optical axis of the corresponding individual optical elements are different between the plurality of light sources, wherein each light source is a surface emitting laser array, and wherein optical axes of the emitted light beams of the light emitting units with different wavelengths are parallel to each other. <EOS>