a current transformer 4 and a current transformer 4 u2032 are provided as in the second embodiment however the connection between the current transformers 4 and 4 u2032 is different from the second embodiment that is the primary sides of the current transformers 4 and 4 u2032 are connected in series and the secondary sides of the current transformers 4 and 4 u2032 are connected in series in the third embodiment of the present invention since the primary sides of the current transformers 4 and 4 u2032 are connected in series the detecting voltage can be twice as great as in the first and second embodiments and the current sensitivity can easily be made to be high with this embodiment even when the reverse current discharged from the first capacitor 3 is very small the voltage applied to the gate of the first transistor 5 is of a high value within the operation characteristics of the first transistor 5 controlling the on off state of the first transistor 5 as mentioned above according to the present invention when a reverse current is detected in the input power supply line the current line is made to be u201c off u201d with this a discharge from a capacitor in the input power stabilizing circuit caused by for example a momentary short circuit.