A 3D model generating system comprising: photographed image acquiring means for acquiring a photographed image in which a first object and a second object each disposed in a real space are captured, the second object being walls of a room in which the first object is disposed; virtual image generating means for generating a virtual image in which a first model (M oj) representing the first object and a second model (M w) representing the second object are disposed in a virtual space, the first object being a standard size, the second object not being the standard size, wherein a virtual camera which acquires the virtual image and a camera which acquires the photographed image have corresponding parameters and viewpoints with respect to, respectively, the second model and the second object; and parameter determining means for performing a determination process to determine a size parameter (λ) indicating a size of the second model (M W), and a position parameter (p j) indicating a position of the first model (M oj), based on a result of comparing the photographed image with the virtual image, wherein the determination process comprises: generating an orientation map of the photographed image and an orientation map of the virtual image, the orientation maps indicating orientations of objects captured in respective pixels of the respective images, based on positional relationships between line segments indicating outlines of respective captured objects in the respective images; masking the first object in the orientation map of the photographed image to generate a first masked orientation map; masking the first model (M oj) in the orientation map of the virtual image to generate a second masked orientation map; and performing a comparison process to compare the first masked orientation map with the second masked orientation map, and adjusting initial values of the size parameter (λ) and the position parameter (p j), based on the comparison process, to increase the coincidence between the first masked orientation map and the second masked orientation map. photographed image acquiring means for acquiring a photographed image in which a first object and a second object each disposed in a real space are captured, the second object being walls of a room in which the first object is disposed; virtual image generating means for generating a virtual image in which a first model (M oj) representing the first object and a second model (M w) representing the second object are disposed in a virtual space, the first object being a standard size, the second object not being the standard size, wherein a virtual camera which acquires the virtual image and a camera which acquires the photographed image have corresponding parameters and viewpoints with respect to, respectively, the second model and the second object; and parameter determining means for performing a determination process to determine a size parameter (λ) indicating a size of the second model (M W), and a position parameter (p j) indicating a position of the first model (M oj), based on a result of comparing the photographed image with the virtual image, wherein the determination process comprises: generating an orientation map of the photographed image and an orientation map of the virtual image, the orientation maps indicating orientations of objects captured in respective pixels of the respective images, based on positional relationships between line segments indicating outlines of respective captured objects in the respective images; masking the first object in the orientation map of the photographed image to generate a first masked orientation map; masking the first model (M oj) in the orientation map of the virtual image to generate a second masked orientation map; and performing a comparison process to compare the first masked orientation map with the second masked orientation map, and adjusting initial values of the size parameter (λ) and the position parameter (p j), based on the comparison process, to increase the coincidence between the first masked orientation map and the second masked orientation map. generating an orientation map of the photographed image and an orientation map of the virtual image, the orientation maps indicating orientations of objects captured in respective pixels of the respective images, based on positional relationships between line segments indicating outlines of respective captured objects in the respective images; masking the first object in the orientation map of the photographed image to generate a first masked orientation map; masking the first model (M oj) in the orientation map of the virtual image to generate a second masked orientation map; and performing a comparison process to compare the first masked orientation map with the second masked orientation map, and adjusting initial values of the size parameter (λ) and the position parameter (p j), based on the comparison process, to increase the coincidence between the first masked orientation map and the second masked orientation map.