In this paper, contact force control of a quadrotor system is presented. Due to an expensive cost of sensors for localization, a camera system is used to locate the quadrotor system. Using a maker on the top of a quadrotor system, heading direction can be justified. Based on the localization, the position control of a quadrotor system is performed in indoor environment. In addition, contact force from a human operator is applied to the quadrotor system so that the feasibility of applying force control to the flying system is tested. Experimental studies of interaction control between a quadrotor system and a human operator are presented to confirm the proposed force control performance.