Recently, Unmanned Aerial Vehicles (UAVs) are applied to various practical tasks such as inspection of deteriorated infrastructures and are expected to survey inside of corrupted buildings in disaster area. In such applications, wired power supply system is useful for extension of task period instead of using on-board battery. In this case, the UAV requires to properly manipulate the power supply cable without inducing any accident, especially collision between the cable itself and environment. This paper addresses collision/obstacle avoidance flight including a cable hanged by UAVs. To accomplish this task, this paper proposes a shape estimation method of a cable using Catenary curve without using tension sensor. The cable is assumed to be flexible, but does not have elasticity. The fundamental flight experiments are carried out to verify the proposed method.