The present invention refers to an optical sensing technique of measuring and controlling a physical quantity of an object present on or in a microstructure by using the Brillouin scattering decrease. In the measuring method, an optical waveguide is prepared linearly or two- or three-dimensionally on or in an element such as a micro chemical chip or an IC chip, and a physical quantity of the object is determined according to the variation of a characteristic of the Brillouin scattering light produced in the optical waveguide.