A disposable tab electrode has core elements that include an adhesive conductive laminate layer and a logo sticker layer with a penetrating hole for contacting a sensor electrode. A protecting film is put around both ends of the core elements. As a result, the disposable tab electrode can be made inexpensively, stored hygienically for a long time and used easily. A lead wire for connecting to the tab electrode has a projection on one end of a sensor electrode that is adhered onto the conductive laminate layer of the disposable tab electrode. The projection is fixed to the lead wire body by a fixing member. As a result, expensive Ag—AgCl electrode sensors can be used repeatedly. The lead wire can have a nipper self-contained or integrated with the lead wire body to prevent the lead wire from separating from the disposable tab electrode during use.