In this paper, we propose a decentralized control system of multiple mobile robots transporting a single object in coordination without using force/torque sensors. In this system, each robot is controlled as if it has a specified impedance dynamics without using a force/torque sensor. The robots transport an object in coordination using a leader-follower type control algorithm. The effect of parameter identification errors is discussed and a method to reduce it is proposed. The proposed control algorithm is experimentally applied to two mobile robots, and the experimental results illustrate the validity of the proposed control algorithm.