Disclosed is a lightning arrester provided for a power transmission line so as to prevent damage to a line-supporting insulator string due to lightning stroke. A lightning arrester unit is fixedly supported on a fitting fixed to an arm structure of a tower in a relation in which its grounded side is electrically insulated from the fitting, and an operation detection device is connected between the grounded side of the lightning arrester unit and the fitting. The operation detection device is in the form of an operation indicator, a flashover indicator and/or an operation recorder. In the event of impartation of a lightning stroke, the operation detection device detects lightning current flowing from the grounded side of the lightning arrester unit toward the fitting.