A first sample solution including exosomes including first to third detection target substances is mixed with a first buffer solution including first nanoparticles including first binding substances which bind to the first detection target substances. The first detection target substances and the first binding substances are bound together, so as to form first complexes of the exosomes and the first nanoparticles. The first complexes are isolated from a mixed solution of the first sample solution and the first buffer solution. The second detection target substances and the second binding substances are bound together, so as to capture the first complexes on a substrate. The second binding substances are fixed onto the substrate. A second buffer solution including second nanoparticles including third binding substances which bind to the third detection target substances is reacted with the first complexes.