1. An endoscopic observation support system comprising: a 3D medical image forming unit configured to form a 3D medical image representing an interior of a body cavity of a subject; a position of interest identifying unit configured to identify a position of a structure of interest in the body cavity in the 3D medical image, the structure of interest being a site of surgical interest or an anatomical structure that requires attention during endoscopic surgery; a position detecting unit configured to detect a real-time position of at least one of an endoscope and a surgical tool inserted in the body cavity; a virtual endoscopic image generating unit configured to generate, from the 3D medical image inputted thereto, a virtual endoscopic image representing the interior of the body cavity viewed from a view point, based on the identified position of the structure of interest and the detected position of at least one of the endoscope and the surgical tool in the 3D medical image, wherein the view point is the position of the structure of interest, the position of at least one of the endoscope and the surgical tool is contained in a field of view of the virtual endoscopic image, and the position of at least one of the endoscope and the surgical tool is shown in an identifiable manner in the virtual endoscopic image; and a display control unit configured to cause a display unit to display the virtual endoscopic image.