Abstract: The present invention is provided with a four-wavelength light emitter that emits four kinds of wavelengths of light toward a predetermined site on a living body; a light receiver that receives the four kinds of wavelengths of light transmitted through the predetermined site on the living body; a received light intensity information acquirer that acquires received light intensity information for the four wavelengths on the basis of an optical signal received by the light receiver; an absorbance time change value acquirer that finds time change values of the absorbances corresponding to the four wavelengths on the basis of the received light intensity information of the four wavelengths; a calibration data table that stores calibration data for finding a predetermined component in blood based on the absorbance time change values; and a component concentration acquirer that finds the concentration of the predetermined component in the blood.