We propose a virtual scuba diving system using an underwater head mounted display (UHMD). This system has two advantages. First, a strong sense of reality is obtained by combining the weightlessness obtained by diving with a highly immersive image presented by a waterproof UHMD. Second, the system is very versatile, such that a user can experience the system in easily accessible waters such as swimming pools or shallow water. In this paper, we describe the design and implementation of the proposed system and the creation of underwater virtual reality (VR) content to provide a diving experience. The proposed system consists of the UHMD with a head tracking sensor, laptop PC, and a hose to protect the cables. The UHMD and laptop PC are connected by cables for power, communication, and video transmission. Each part is waterproof. The created VR content makes it possible to freely swim in the virtual undersea world by head tracking and operation of the controller. We conducted a pilot experiment to test the proposed system while users swam in a pool of about 4 m in depth. The UHMD was confirmed to have sufficient waterproofness at water depth of about 4 m. It is also suggested that it is possible to create the illusion that the water depth in the virtual underwater space is the user’s own water depth.