Abstract: Provided is a display device including: a viewpoint tracker for detecting a viewpoint variation by tracking a user's viewpoint; a display for alternately displaying a right image and a left image corresponding to user's right eye and left eye; a parallax barrier consisting of sub-segments which are continuously arranged to transmit or block the images by electrical on or off and alternately turned on/off by the unit of groups to alternately form an image transmission region and an image blocking region, in order to provide a 3D image by separately transmitting the right image and the left image to the user's right eye and left eye; and a barrier controller for electrically moving the image transmission region and the image blocking region of the parallax barrier by the unit of sub-segment according to the viewpoint variation, and a method for providing a 3D image of the display device.