A first temperature sensor is formed in a first measurement area. A first input part is formed in the first measurement area so that an output surface thereof is exposed to the inner surface of the liquid tank. A first light receiving part receives a reference light through the liquid from the first input part. A second input part causes a second incident light to be incident on a living body. A second light receiving part receives a measurement light from the second input part. Based on the light intensity of the reference light and the measurement light, an absorbance calculation device can detect the absorbance of the liquid and living body tissue. A concentration calculation device compares the absorbance of the liquid with the absorbance of the living body tissue and calculates a concentration of a measured component contained in the living body tissue.