The study develops a portable interface system to inform berthing operators of the position and heading in relation to the quay when berthing a large vessel equipped with distance-measuring instruments. A portable interface system is indispensable for preventing collisions and improving the efficiency of berthing operations because it allows operators to intuitively grasp the movement status of the vessel based on the distance data measured during berthing. These data can not only be converted into the current position and heading of the vessel relative to the quay, but can also be visualized to predict the movement and speed of the vessel in a few seconds. Therefore, we developed a visualization system using Rviz, a 3D model visualization tool for a robot operating system, and verified the necessity for an interface system through simulations and experiments using a model vessel. Furthermore, we extended the function of the visualization interface using a wireless network, developed a web application to display the vessel’s positioning information on multiple operators’ terminals, and verified the drawing stability at 10 Hz using the extended application.