1. An insertion support system comprising: virtual image generating unit for generating three-dimensional images of a duct in a body cavity in a subject as successive virtual images in frame units, on the basis of image data of a three-dimensional region in the subject; navigation image generating unit for generating a navigation image including an endoscope image sent by an endoscope configured to capture images of the duct in the body cavity in the subject, the virtual image, and a plurality of reduced size images of the virtual image at all branch points at which the duct in the body cavity in the subject diverges; rotation information storing unit for storing image rotation information of the reduced size images; and image rotation controlling unit for rotating the reduced size images generated by the navigation image generating unit, on the basis of the image rotation information.