The detector comprises a loopback unit 10 which is connected to a connector formed at one end of an optical camera cable, an optical loop fiber 11 connecting a first optical fiber 31 and a second optical fiber 32, and a short-circuit wiring 12 which short-circuits plural electric lines of the optical camera cable. The detector also comprises a measuring unit 40 comprising a transmission loss measuring part which is connected to a connector formed at the other end of the optical camera cable and measures transmission loss between the first optical fiber and the second optical fiber, a resistivity measuring part which measures resistivity between electric lines, a disconnection detecting part which detects connection or disconnection of electric lines by using measured resistivity, and a display part, which displays the result of transmission loss measured by the transmission loss measuring part and connection or disconnection detected by the disconnection detecting part.