A display device having an A/D (Analog/Digital) converter receiving a signal from a personal computer (PC) and converting the signal into a digital signal a decoder receiving external input signals from an external signal inputter such as a TV or a Video player that decodes the external input signals into the digital signal, and a video processor that performs a PIP (Picture In Picture) signal process displaying one of the PC signal converted and the decoded external input signal as a main screen and the other one as a sub main screen, thereby enabling the converted PC signal and the decoded external input signal to be displayable on a display. The display device also has a memory storing different display property values depending on the external signal inputter setup; and a controller controlling the PIP signal process of the video processor based on an external signal, reading the display property values from the memory, and controlling the decoded external input signal to be converted depending on the read display property values.