Abstract: [Problem to be Solved] A biosensor having high detection sensitivity and detection specificity is provided. [Solution] There is provided a biosensor comprising: an identification substance capable of binding to a substance to be detected; and an electrode charged with a charge of the identification substance, and detecting a change in a charge density of the electrode caused by binding of the substance to be detected to the identification substance, wherein a polymer layer in which a molecular template having a structure complementary to a molecular structure of the substance to be detected is formed is formed on all or part of a surface of the electrode, the identification substance is contained in the polymer layer, and the polymer layer is an ultrathin film layer.