Presentation of images showing with high resolution the state of a surgical field during surgery is realized with a simple configuration. When performing surgery, a three-dimensional model is generate based on MRI images of a patient captured prior to surgery, and three-dimensional coordinates of each location on a surface of the patient are measured by scanning a laser beam over the surface and detecting laser beam reflected therefrom, and correspondence is made with the MRI image for each location of the surface (frameless/markerless: steps 100 to 116), the position of a surgical instrument is also detected by the laser beam, the position of the surgical instrument derived, and images of the surgical instrument combined onto the MRI images and displayed during surgery (steps 120 to 130).