The mechanical systems composed of the power-circulation structure exist in the field of industrial machines, and the powers of two or more motors of the same output are synthesized through the gear stages to drive the driven machine part and the desired motion of the machine is achieved. However, in the mechanical system with a power-circulation structure, the residual vibration related to the natural frequency in the lower-frequency range will be generated when the motor starts or stops. This phenomenon causes problems such that the productivity of the mechanical system will be reduced. In this paper, the case that the power-circulation mechanism is driven by two motors is taken up, and the vibration suppression control of this mechanical system is investigated by simulations. In the other paper of author at this conference, the effect of the sensor-based control was confirmed by using the performance evaluation index composed of the control error and current consumption areas. On the other hand, in this paper, the disturbance suppression performance is investigated. The author proposes a control method to switch the control mode between starting/stopping and steady state of rotations. Simulations show satisfactory control results to reduce the residual vibration at starting/stopping and the angular speed fluctuation when the disturbance is exerted at the driven machine part.