An initial registration unit performs initial registration between an intraoperative image and simulation information. A positional information obtaining unit obtains positional information indicating a relative positional difference between the intraoperative image after the initial registration and a newly obtained intraoperative image based on an unchanged position which is not changed during surgery included in the intraoperative images. A superimpose display unit registers the simulation information with the new intraoperative image based on the positional information and displays, on a display, the simulation information superimposed on the new intraoperative image.