The present invention relates to a method for detecting an antigen with use of an antibody and an enzyme. Specifically, the present invention provides a method for detecting an antigen without use of a labeled-antibody. the method comprises immersing particles in a first buffer solution which is predicted to contain the antigen; wherein an antibody and a multi-copper oxidase CueO are immobilized on each surface of the particles, and the antibody reacts specifically with the antigen. The method further comprises the following steps recovering the obtained particles; mixing the particles recovered, an oxidation-reduction indicator (reductant), and a second buffer solution so as to prepare a reaction solution; measuring an activity degree of the multi-copper oxidase CueO contained in the reaction solution; determining that the first buffer solution contains the antigen based on the above activity degree.