We have developed the first prototype system of a neurosurgery simulator. It is developed for amedical training of cerebral aneurysms operation. This paper describes the artery model of the simulator. The system is equipped with a binocular microscope type of stereo view display, a foot pedal for its manipulation, and input devices as surgical tools such as spatula and clip. As for the procedure, operators first move arteries with a spatula in the left hand and take a cerebral aneurysm to a proper position. Then they pick up the aneurysm firmly with a clip in the right hand, and release the tip of the clip, which remains at the aneurysm position. In order to simulate the surgery in real-time, spring based model is adopted for an artery deformation and a simplified model is for surgical tools. Both models are approximated as line segments. As a result, the collision detection problem is dolved as intersection calculation of two line segments. The performance could reach to 37 Hz. The next target is a network-based remote education system with haptic device.