In this paper, rolling motion of Denguribot that is rounded two-link robot is improved to performance. Rolling motion of Denguribot has been already achieved by using input-output linearization. In the previous research, reference paths for each phase of rolling motion are designed intuitively. As a result, the output zero is not kept at the phase transition and peaked input is required to control. This paper proposes smooth reference path with respect to the relative degree of the virtual output, and the validity of proposed method is verified via numerical simulation.