This paper presents several display systems for augmented reality (AR) developed by the author’s group. All of them are based on sensing the three-dimensional position of user’s gaze (3D gaze), and they are AR user interfaces that provide some benefit to the user without the user's intention to operate the systems. In particular, we focused on the depth of a user's gaze for (1) presenting a more realistic representation of depth of focus, and (2) gaze-driven AR x-ray vision to make real objects semi-transparent and show the hidden parts. Additionally, an application example for an in-vehicle AR display is shown as a situation where such technology will be necessary or important in the near future.