Medical information including medical images are used for surgical navigation system, however, surgeon often encounter the difficulties to obtain a precise registration between pre-operative information and the patient. In this paper, we propose to apply “augmented reality system” with a simple display device. It's comprised of a 5.6inch LCD, a half mirror, and a frameless positioning maker system. Through the half mirror, surgeon can observe the real patient and reflected image of the LCD, on which the navigation image are shown simultaneously at the right position floating inside the patient body to perform minimally invasive surgery. System precision including human perception error are evaluated using phantom experiments and the total result are 1.96±1.28mm and the pilot trial in the operating room are performed toward clinical use.