This paper describes a method of a sensorless force control of direct-drive robot which has three-degrees-of-freedom. In the proposed method, a disturbance observer, which estimates the total sum of disturbance effects, is employed in each joint. First, the robust motion controller is realized by the feedback of the estimated disturbance torque. Secondly, the reaction force (reaction torque) is calculated from the estimated disturbance torque and the motion equation of robot. Finally, the calculated reaction force is fed back to obtain the sensorless force controller. This method is so simple that the total algorithm is executed in the on-line calculation. Several experimental results' are also shown to confirm the validity of the proposed method.