A device and a method for automatically discriminating formats of video signals input to a monitor and processing the respective signals in accordance with the identified formats are provided. The device automatically identifies whether signals input to the same input port are RGB type PC signals or YPbPr type HDTV signals and processes the signals in accordance with the identified formats. Therefore, users have only to install a single input port commonly used to receive PC signals and HDTV signals rather than installing separate input ports for separately receiving PC signals and HDTV signals.