A sensor chip has a metal layer formed on a surface of a substrate, where a plurality of microscopic concave part is formed in a measurement region of the surface of the metal layer. When light of linear polarization is irradiated onto the measurement region, local resonance electric field generates at opposing metal layer surfaces in the concave part. The reflected light thereof is received to measure reflectance. The light of linear polarization is irradiated so that the polarizing surface becomes orthogonal to the longitudinal direction of the concave part.