A detection device of a planar area is provided. The detection device includes an image obtaining section for obtaining a left image and a right image; a planar area aligning section for setting given regions of interest to the obtained left image and the right image, and through use of a geometric transform function that matches the region of interest of the right image with the region of interest of the left image, performing geometric transform to generate a geometric transform image; and a planar area detecting section for detecting a planar area based on the geometric transform image and the region of interest of the right image. The planar area aligning section sets the planar area detected by the planar area detecting section as a given region of interest.