A concept on realizing impedance-based motion control of a passive type robot for transporting a single object in coordination with a human operator is proposed in this paper. We developed a prototype of passive type robot referred to as RT Porter, which consists of mobile frame equipped three omnidirectional wheels with MR Brakes, and on-board computer system. In this research, we control the brake torque of each wheel based on the brake force/moment constraint so that impedance characteristics is realized on RT Porter with human's pushing. This allows RT Porter to move in a 2D path, which includes motion perpendicular to human's pushing direction without using servo motors. Experimental results are shown to illustrate the validity of the proposed concept.