Magnetic-field generating elements or magnetic-field detecting elements are fixed into an insertion part having elasticity, which is inserted into a subject, by an insulating material while ensuring that forms of the respective magnetic-field generating elements or the respective magnetic-field detecting elements are not changed. Even when the insertion part is bent, there is no change in either the function of magnetic-field generation or the function of magnetic-field detection. Magnetic-field detecting elements or magnetic-field generating elements which are arranged at known positions around the subject are combined with each other to calculate three-dimensional positions of the magnetic-field generating elements or the magnetic-field detecting elements within the insertion part. Further, a form of the insertion part is estimated, and a three-dimensional image corresponding to a form of the insertion part is produced. Moreover, a three-dimensional image is projected onto a screen surface to display a stereoscopic image corresponding to the form of the insertion part.