D. Zhou et al. proposed an algorithm based on the buffered Voronoi cells (BVC) for quadrotors to reach each given target position without mutual collision. However, in the method, it is assumed that all quadrotor positions are known and the control inputs for all quadrotors are calculated in a single computer. In this paper, we describe the method to compute the Voronoi diagram using only the obstacle information around a quadrotor in an unknown environment and to reach a given target position. The usability of this method is confirmed by simulation.