Parallel wire suspended system has a large weight capacity and wide range of movement as a positioning mechanism for heavy objects. In many researches of parallel wire suspended system, a sag of wire has been ignored. However, it seems that using the model that taking into account a sag of wire improves accuracy of the position control of parallel wire suspended system. In this paper, a calculation method of kinematics and stiffness takes into consideration a sag of wire is proposed. Using this method, it is shown that light weight of suspended object and high linear density of wire make large displacement by a sag and reduce the stiffness of the system.