Abstract: Clicking on a virtual object is the most fundamental and important interaction in augmented reality (AR). However, existing AR systems do not support natural click interfaces, because head-mounted displays with only one camera are usually adopted to realize augmented reality and it is difficult to recognize an arbitrary gesture without accurate depth information. For the ease of detection, some systems force users to make unintuitive gestures, such as pinching with the thumb and forefinger. This paper presents a new natural click interface for AR systems. Through a study investigating how users intuitively click virtual objects in AR systems, we found that the speed and acceleration of fingertips provide cues for detecting click gestures. Based on our findings, we developed a new technique for recognizing natural click gestures with a single camera by focusing on temporal differentials between adjacent frames. We further validated the effectiveness of the recognition algorithm and the usability of our new interface through experiments.