1. An image capturing device that displays a length of an object based on a first image in which the object is photographed and parallax information corresponding to the first image, the image capturing device comprising: a length calculation circuit that calculates the length of the object; an object comparison circuit that calculates, as a length magnification A, a ratio of the length of the object to a length of a comparison object that is compared with the object; and an image composition circuit that combines the first image with a second image to generate a third image and outputs the third image; wherein the second image is formed by converting a fourth image of the comparison object based on the length magnification A calculated by the object comparison circuit; the image composition circuit combines the first image with a fifth image to generate a sixth image and outputs the sixth image; and the fifth image displays that the length of the object is A times the length of the comparison object.