The present invention addresses the problem of providing: a means for applying an electrically conductive polymer onto a base material directly and with high efficiency so that the electrically conductive polymer can be used as an electrode element without being bled when PEDOT-pTS is used as the electrically conductive polymer； a surface electrode which is produced without using an electrically conductive gel, has excellent electrical conduction performance and therefore can have a reduced surface area, can be adhered onto skin, does not undergo the displacement on skin even upon the application of a little movement of a body, and can be used in myoelectric signal measurement systems and brain wave measurement systems that have been used in various situations of life. Provided are: a method for producing an electrode element, said method being characterized in that a mixed solution of (1) an organic solvent-based solution containing an oxidative component and p-toluenesulfonate (pTS) and (2) 3,4-ethylenedioxythiophene (EDOT) is brought into contact with a base material to adhere the mixed solution onto the base material and then the contact part is subjected to a polymerization acceleration treatment in synchronization with the contacting； and a biopotential electrode to be applied onto a surface or to be punctured upon use, said biopotential electrode being characterized by comprising the electrode element.Le problème de la présente invention concerne : un moyen pour appliquer un polymère électroconducteur sur un matériau de base directement et avec une efficacité élevée, de telle sorte que le polymère électroconducteur peut être utilisé comme élément d'électrode sans être purgé lorsque du PEDOT-pTS est utilisé en tant que polymère électroconducteur ； une électrode de surface qui est produite sans utiliser de gel électroconducteur, qui présente une excellente performance de conduction électrique et qui peut par conséquent présenter une aire de surface réduite, qui
