Dementia caused by vascular disorders in the brain, e.g., Alzheimer’s disease and vascular dementia, develops after long-term pathological changes in the brain. Thus, dementia prevention requires continuous long-term efforts. In this study, we developed a dual-task virtual reality (VR) system that utilizes a motion capture device and a VR head-mount display device to enable users to perform cognitive tasks in a VR environment while moving their bodies. In the proposed system, the motion capture device detects and captures the user’s whole-body movements in real time, which are then synchronizes with an avatar in the VR environment. In addition, the users can experience the proposed system in a game-like manner by selecting the correct object by moving their body against four-choice calculation problem objects that appear moving forward in the VR space.