This paper presents a distributed motion control method to keep communication distance between mobile agents which equip any wireless communication devices for the sake of their cooperative tasks. Because the wireless communication range is inherently limited due to an upper bound of transmission power, the agents should move carefully in order not to disconnect the communication links. In this study, we try to construct a distributed cooperative link keeping constraint in velocity space, by reference to a reciprocal velocity obstacle method which is used for computing a collision avoiding velocity. We can find the agents with the proposed constraint moves naturally (oscillation-free). Our method does not limit original tasks of the agents since the method only provides a velocity bound constraint, therefore it seems suitable for several cooperative tasks.