There is provided a cochlear implant for improving the hearing ability of a patient suffered from hearing impairment comprising an internal receiving unit implanted into the body, which comprises a receiving part for receiving external signal, an active electrode and a reference electrode, characterized in that the active electrode is constructed with a single electrode wire having different thickness in at least two different regions. The active electrode of the internal receiving unit is inserted into a space formed at between the mastoid bone and the ear canal skin and end of the active electrode is inserted into the scala tympani of the cochlea and directly stimulates spiral ganglion. The cochlear implant provides easier implantation into the body and improved hearing ability at a lower cost.