In this paper, we study cooperative control problems with a multi-UAV system expressed as a fourth-order system using a consensus algorithm. We first show that a linearized model of quadrotors is expressed as a fourth-order system, and then propose a formation control algorithm for the fourth-order system after formulating a problem. The proposed control law is based on a consensus algorithm and a leader-follower structure is also applied to the control law so that a leader can individually provide each of the quadrotors with information of their desired states. And then, we show that the proposed control algorithm can guarantee accurate formation keeping when fundamental assumptions about the network composed of the multiple UAVs are satisfied. Finally, the proposed approach is validated by some simulations.