The present invention relates to a method for connecting electrodes comprising: interposing the polyphthalide represented by the formula (I): ##STR00001## wherein R represents a divalent aromatic hydrocarbon group or a divalent heteroring-containing aromatic group, R.sub.1 represents an alkyl group, a fluorinated alkyl group, an alkoxy group or a halogen atom, where the number of R.sub.1 is 0 to 4, X represents O or N--R.sub.3, provided that R.sub.3 represents one of the following groups, ##STR00002## Y represents SO.sub.2 or Co and n represents a number of repeating units in the polymer, as a pressure-sensitive conductive polymer at least partially between electrodes opposed to each other; and applying a pressure to fix the both electrodes, a surface-treated wiring board comprising polyphthalide represented by the formula (I) formed on at least part of the surface of the electrode part, an adhesive film comprising an adhesive and polyphthalide represented by the formula (I), and an electrode-connected structure using the same.