Abstract: The present invention provides a single-cable transmission device for signals and a power supply of a surveillance system, which only requires a single cable to transmit various signals and a power supply; which transmits signals in a carrier manner, allowing longer-distance transmission; which transmits signals in a frequency division manner, allowing bi-directional transmission. A power-supply-voltage/output-load status display is further provided, thereby facilitating a user to directly find the cause of a failure so as to eliminate the failure promptly.