By applied electric field mixing (EFM) showed antigen-antibody reaction time in an immunohistochemical staining can be shortened from 90 minutes of conventional method to 10 minutes. In this study, EFM examined the mechanism which makes antigen-antibody reaction of an immunohistochemical staining quicken. As a result, we obtained that it has the mechanism which a reaction time of an immunohistochemical staining is shorten because antigen and antibody improve to increase the frequencies of contact under EFM compared with conventional method. Further, we investigated the effect of AC electric field is applied on antibody. As a result, it found that by applied AC electric field to antibody liquid, antibody dispersed and stabilized, therefore, staining quality is improved.