The disclosed electrode device for high frequency thermotherapy apparatus comprises a base member; a cavity-inserted cylindrical body removably fixed to the base member and inserted into a cavity of a living body; a separator fixed to the base member and arranged in the cylindrical body, for partitioning a space within the cylindrical body into two; an electrode arranged at an end of the separator; and in particular a circulation passage for a cooling liquid being formed extending from a going path, through an end space, to a return path within the cylindrical body. Therefore, the surface of the living body in contact with the cylindrical body can be efficiently cooled by circulating a cooling liquid therethrough to protect the surface of the living body from being heated excessively. Further, the cavity-inserted cylindrical body can be replaced or removed for washing to realize a sanitary medical treatment.