A concentration measuring device, the measuring light in a wavelength region where an absorbance related to the water in the subject can be practically ignored is irradiated to the subject S by a light source. The transmitted light that was transmitted through the subject S is received in a light receiving part. An optical rotation calculation part calculates an optical rotation of the subject S by using an output signal from the light receiving part, and an absorbance calculation part calculates an absorbance of the subject S by using an output signal from the light receiving part. A concentration calculation part calculates a concentration of glucose by using a glucose measurement data related to an aqueous solution of simple glucose, a protein measurement data related to an aqueous solution of simple protein, the optical rotation calculated by the optical rotation calculation part, and the absorbance calculated by the absorbance calculation part.