In this paper, we assume a situation that multiple quadrotors are flying autonomously in the same space for the purpose of aerial photographing, surveillance, or home delivery and so on. In such a situation, an algorithm to avoid mutual collision is needed. D. Zhou et al. proposed an algorithm based on the Buffered Voronoi Cells (BVC) to reach each target position without mutual collision when the multiple quadrotors fly and confirmed its operation by some simulations. In this research, we applied the method based on BVC to the different number of quadrotors from the verification by D. Zhou et al. and verified the performance of it by numerical simulations using MATLAB. In addition, we confirmed the algorithm by a dynamic simulation with four quadrotors using the dynamic simulator V-REP.