When people walking exercise alone, there are problems with difficult to maintain and increase the motivation. We investigated the effectiveness of interactions with a 3D personalized avatar in Augmented Reality to increase the motivation of walking exercise. Our system proposed novel interactions in walking scene with 3D personalized avatar as a virtual walking partner. We designed the interactions among user, 3D avatar and physical world in walking exercise scene. In addition, our system has novel method of movement synchronization between user and 3D avatar using AR HMD （Microsoft HoloLens2）. As a result of the preliminary evaluation, we found the positive results of the usability and effectiveness of the system.