An RF converter circuit 11 that constitutes a video signal superposing/power deriving unit 100 converts video signals generated from images taken by a surveillance camera 10, which derives a direct current voltage as a driving power from an antenna lead-in wire 6 through a filter circuit (LPF circuit 12), to radio-frequency signals. The radio-frequency signals are transmitted through the antenna lead-in wire 6 to a television receiver 2. Images taken by the surveillance camera 1 can be viewed on the television receiver 2 only by selecting the channel assigned to the surveillance camera 1. Accordingly, the driving power for the surveillance camera 1 is not relied upon a solar battery or secondary batteries, and wiring work therefor may be simplified.