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 user's 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 mixed image signal to the user for displaying thereof.