This paper deals with the experimental characteristics of the behaviors appeared in the multi-robot system in the course of communication network expansion and returning behaviors. We assign the task to search for and to carry a target back to the nest to the multi robot system. The robots have no global information about the location of the target, boundaries and itself. To accomplish the task the multi-robot system constructs by themselves a communication network in the given maze area and the robots finding a target return to its start area along the communication network. We examine experimentally the characteristics of the communication network expansion and returning behaviors of the multi-robot system using 40 hardware robots with respect to some of important indexes expressing the performance of the mulit-robot system. As conclusion, this paper demonstrates experimentally the emergence of robot group intelligence caused from the dynamic interactions between robots and the environment.