The user is allowed to more reliably recognize a positional relationship and a relative approach between an endoscope and a site of interest, such as a surgical tool or a site of surgical interest, during observation of a body cavity of a subject using the endoscope inserted in the body cavity. A virtual field of view determining unit (26) determines a virtual field of view of a virtual endoscope positioned at a position in a 3D medical image corresponding to a position of an endoscope detected by an endoscope position and posture detecting unit (11), based on a position of a structure of interest identified by a position of interest identifying unit (24), a corresponding position and a posture of the endoscope, and an angle of view of the endoscope obtained by an endoscope angle of view obtaining unit (25), such that the position of the structure of interest is contained within the virtual field of view and the virtual field of view has continuity with the field of view of the endoscope. A virtual endoscopic image generating unit (27) generates, from the 3D medical image formed by a 3D medical image forming unit (5) and inputted thereto, a virtual endoscopic image having the determined virtual field of view with the view point thereof being the corresponding position of the endoscope. A display control unit (27) causes a WS display (10) to display the generated virtual endoscopic image.
