The present invention enables to classify and measure two or more kinds of target substances which have the same recognition site recognized by a specific capturing body. Specifically, by using a target substance detecting element for detecting two or more targets, whose kinds are different mutually, at the same time, the target substance detecting element, characterized by having a base material, two or more kinds of metal structures provided on a surface of the base material, and a target capturing body provided on each surface of the two or more kinds of metal structures, and in that the number of kinds of the metal structures are equal to or more than the number of kinds of the target substances, concentrations of the two or more kinds of target substances can be calculated by integrating and analyzing detection signals detected from the target substance detecting element.