To provide a power circuit normally starting even a monitor camera having a large power consumption and being capable of also responding even to a load fluctuation.

The monitor camera is connected by one cable for a system superimposing a power-supply current on a video signal. The monitor camera has an impedance converter converting the impedance of an input current, and a large-capacity capacitor connected at the rear of the impedance converter. The monitor camera further has a voltage detector connected at the rear of the large-capacity capacitor. In the monitor camera, internal power supplys for supplying a circuit for operating the monitor camera with the current are started successively when a voltage at a certain threshold value is detected by the voltage detector.

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