A recording/reproducing apparatus with a surveillance function includes a first signal input terminal for receiving video signals from an image-capturing device; a second signal input terminal for receiving TV signals from a TV signal source; a control circuit coupled to the first and second signal input terminals for processing the video signals and/or the TV signals and executing a comparing procedure of the video signals, and when a first video signal and a second video signal sequentially received via the first signal input terminal have a difference greater than a threshold, converting the second video signal into a written data; and a storage device coupled to the control circuit for storing the written data.