Abstract: An excitation beam generated from a light source is separated into a measuring beam and a reference beam by an optical path adjusting optical system including a beam splitter, so that the measuring beam is applied to a sample in a cell. Raman scattering light which is generated from the sample is detected by a spectral detector including a spectroscope through a scattering light path adjusting optical system and a wavelength selector. In a spectrum obtained by the spectral detector, a peak of Raman scattering in which wavenumber shift from the wavelength of the excitation beam is present at 800 to 920 cm.sup.-1 is employed to make quantitative measurement of hydrogen peroxide. Hydrogen peroxide contained in an aqueous solution can be simply quantitatively analyzed through optical analysis means.