To enlarge the magnetomotive force so that the performance level does not drop by converting the induced voltage, which is generated at the secondary side of a current transformer where the primary winding of the integrated structure of core is made of the conductor for shunting the current flowing to a stringing, into DC voltage and changing a storage battery with it.

A current transformer 1 is one where copper strand 1b is wound on the primary side of an integrated type of core 1a, an enamel wire 1c is wound on the secondary side, and a rectifying circuit 2 is connected to both sides of the enamel wire 1c. A charging circuit 3 is equipped with an overcurrent preventive circuit, consisting of a diode 3c for limiting the current outputted from the rectifying circuit 2 and a DC resistor 3b and limits the charge current during the charging of the storage battery 3c by the DC resistor 3b, and when the terminal voltage of the charged storage battery 3c becomes equal to the voltage of the anode of the diode 3a, the charging is stopped. Accordingly, there is no factors in performance level drop, such as water penetrating into the division face and rust occurring, etc., and sufficient magnetomotive force for charge the storage battery can be obtained as compared with before.