The object is to provide an environment in which dynamic verification of harness design is available, and thereby realizing efficient harness design. The apparatus comprises: a mechanism information storing unit which stores in advance three-dimensional model data of a mechanical component, other than the harness, of the object apparatus; a harness information setting section which sets harness information; a simulation section which creates a three-dimensional mechanism model of the harness and of the mechanical component based on the harness information and on the three-dimensional model data of the mechanical component, and which simulates motion of the harness in conjunction with motion of the mechanical component using the three-dimensional mechanism model; a display; and a display controlling section which controls the display to show thereon the simulation result obtained by the simulation section.