Abstract: To control information obtained from inside of a living body with higher precision as compared to that in the conventional technology by controlling a ratio of intensities of light, directed to a trial body, in a plurality of wavelength ranges different in peak wavelength from each other, a measurement error included in information obtained from the living body can be controlled by changing a ratio of intensity of the light in the first wavelength range against that of the light in the second wavelength range. When intensity of irradiated light is limited from the viewpoint of safety to the trial subject, by keeping a ratio of the light irradiated to the trial body in the first wavelength range against that of the light in the second wavelength range under a prespecified value and also by changing the ratio of irradiated light intensities under the prespecified value, a measurement error included in information obtained from the living body can be controlled.