A fine structure body comprising first fine metal particles, which have head regions projected upwardly from a surface of a base body, is utilized. A substance capable of undergoing specific binding with a test body is fixed to the head regions of the first fine metal particles. Second fine metal particles, to which a substance capable of undergoing specific binding with the test body has been fixed, are dispersed in a sample liquid. The test body is detected from variation of a resonance wavelength of localized plasmon resonance, which variation occurs when the test body is adsorbed to the surface of the fine structure body by being sandwiched between the substance fixed to the first fine metal particle and the substance fixed to the second fine metal particle.