A coil spring modeling apparatus includes a first attachment member disposed on a lower spring seat, a second attachment member disposed on an upper spring seat, an actuator unit formed of a Stewart-platform-type parallel mechanism, a spring height detection mechanism, and a controller. The spring height detection mechanism is constituted of displacement gauges such as a linear variable differential transformer. These gauges are provided on hydraulic cylinders, and detect amounts of displacement relative to the reference lengths of the hydraulic cylinders, respectively. A hydraulic pressure supply device is controlled by the controller and supplies fluid pressure according to the displacement detected by the gauges to the respective hydraulic cylinders.