An image completion system for an in-image cutoff region, comprising: a main imaging device configured for obtaining a main image in which an object space to be monitored is imaged; a completing-purpose imaging device configured for obtaining a completing image used for completing the main image by imaging the object space in a line-of-sight direction different from that of the main imaging device; and an image processing device configured for completing a portion of the main image with the completing image on the basis of three-dimensional positions of set points which are set in the object space and three-dimensional positions of the main imaging device and the completing-purpose imaging device, a distance measuring device configured for measuring separating distances between the set points and a predetermined reference point; and a three-dimensional position measuring device configured for measuring three-dimensional positions of the main imaging device and the completing-purpose imaging device, wherein the main imaging device and the completing-purpose imaging device are provided so as to image the object space almost simultaneously, wherein the image processing device is configured for obtaining from the completing image, image information on a cutoff region in the object space that is hidden behind on a depth side of a member having a known shape by imaging the member in the main image together with the object space, on the basis of information on the three-dimensional positions that are continuously detected, and for replacing image information on the member in the main image with the obtained image information or superimposes the obtained image information onto the image information on the member in the main image so as to generate a composite image in which the cutoff region is completed with the completing image, and wherein the image processing device is configured to complete a portion of the main image with the completing image on the basis of measurement results from the distance measuring device and the three-dimensional position measuring device. a main imaging device configured for obtaining a main image in which an object space to be monitored is imaged; a completing-purpose imaging device configured for obtaining a completing image used for completing the main image by imaging the object space in a line-of-sight direction different from that of the main imaging device; and an image processing device configured for completing a portion of the main image with the completing image on the basis of three-dimensional positions of set points which are set in the object space and three-dimensional positions of the main imaging device and the completing-purpose imaging device, a distance measuring device configured for measuring separating distances between the set points and a predetermined reference point; and a three-dimensional position measuring device configured for measuring three-dimensional positions of the main imaging device and the completing-purpose imaging device, wherein the main imaging device and the completing-purpose imaging device are provided so as to image the object space almost simultaneously, wherein the image processing device is configured for obtaining from the completing image, image information on a cutoff region in the object space that is hidden behind on a depth side of a member having a known shape by imaging the member in the main image together with the object space, on the basis of information on the three-dimensional positions that are continuously detected, and for replacing image information on the member in the main image with the obtained image information or superimposes the obtained image information onto the image information on the member in the main image so as to generate a composite image in which the cutoff region is completed with the completing image, and wherein the image processing device is configured to complete a portion of the main image with the completing image on the basis of measurement results from the distance measuring device and the three-dimensional position measuring device.