Multi-robot systems are expected to improve the ability of processing tasks, a work efficiency, and an extendability of a robot system by cooperating each other. However, using multiple robots complicates its control system. As one of the associated problems, robot movements are picked up. Since a robot formation is useful to transfer multiple robots to their destinations effectively, many studies have been performed. This paper describes a method, which is called "IET method," for forming a formation with multiple robots. The method can specify the position of each robot in a group and change the shape of a formation. Note that each robot is assumed to have different ability and identified each other. Alternatively, the method needs a system that obtains the ID and relative position of the robots. We describe how to construct the measurement system using wireless communication and ultrasonic sound, and evaluate it through some simulation experiments.