1. A vehicle environment monitoring device, comprising: an imaging section for taking image data of an environment of an automobile, the image including at least two types of colors; a setting section for setting a specific area of the image data obtained by the imaging section, wherein the specific area has a strip shape longer in, and parallel to, a horizontal direction of a frame image and includes at least two types of colors; an extraction section for taking in image data of the specific area in units of one or a plurality of frame images taken by the imaging section in time series and extracting moving vector information based on the image data of the specific area; and a detection section for detecting a second vehicle which is present in an environment of a first vehicle having the vehicle environment monitoring device mounted thereon, based on the moving vector information.