A displaying apparatus includes a connector having a DDC communication pin which communicates with a video card provided in a computer main body, a video signal processing unit which processes picture signals supplied through the connector, a power circuit unit which converts commercial alternating current (AC) power into driving voltages, and a controlling unit which controls power supplied to each of signal processing units from the power circuit unit to be on or off in response to existence or non-existence of DDC voltage signals input through the DDC communication pin of the connector. Accordingly, power of the displaying apparatus is controlled to be on or off in response to a power-on or off state of the computer main body, and allows the power thereof to be consumed at a minimum level under the condition of a stand-by power mode.