1. A display apparatus for a mixed reality environment, comprising: an external image processor for mixing an actual image of an object around a user and a single or plurality of artificial stereo images artificially created to provide a multiple external image signal; a user information extractor for extracting the users visual information; an image creator for creating a stereo image signal based on the extracted user's visual information; an image mixer for synchronizing the multiple external image signal and the stereo image signal; and an image output unit for outputting the synchronized multiple external image signal and stereo image signal to the user for displaying thereof by use of a light source, wherein the user information extractor tracks eyes of the user without having a separate light source by use of the light source of the image output unit for outputting the synchronized multiple external image signal and stereo image signal to the user.