The present invention provides the following: a method for efficiently producing a reagent for detecting an antibody that specifically binds with an insoluble antigen protein present in a liquid sample; a reagent for antibody detection produced by the production method; and a use of the antibody. In a step for solubilizing an antigen protein, it is possible to efficiently solubilize and recover the antigen protein by using a cationizing agent; therefore, when compared to conventional methods, it is possible to efficiently produce a reagent for detecting an antibody that has bound to multiple antigen protein molecules in a carrier.