Abstract: A reflection type oximeter comprises light emitting diodes (11 to 16) as first to sixth light sources which emit first and second beams of a wavelength involving a change in absorption due to a change an oxygen saturation of hemoglobin in blood of a tissue of a living body, third and fourth beams of another wavelength involving no change in absorption, and fifth and sixth beams of a further wavelength involving a relatively small change in absorption due to changes in a quantity of hemoglobin an oxygen saturation. The beams ae applied to the body tissue and the beams of the first to sixth light sources reflected by the body are received by a light receiving element (17). Intensities of the beams emitted from the light emitting diodes are set to predetermined levels and the intensities of the beams received by the light receiving element are evaluated by a CPU (23). Based on a predetermined function, the quantity of hemoglobin and of the oxygen saturation of the body tissue are evaluated.