1. A vehicle surroundings monitoring apparatus that extracts a body present in the surrounding of a vehicle as an object, based on an image captured by an infrared imaging device, comprising: a binarized object extraction device that extracts a binarized object from image data obtained by binarizing a gray scale images of the image; a search region setting device that sets a plurality of search regions vertically using a predetermined height as a reference around the binarized object extracted by the binarized object extraction device, in the gray scale image; a search region extraction device that extracts a search region having a distance to the infrared imaging device substantially equal to a distance between the binarized object and the infrared imaging device, among a plurality of the search regions set by the search region setting device; a correlation degree determination device that determines a degree of correlation between the plurality of search regions extracted by the search region extraction device; a height calculation device that calculates a height of the binarized object in the gray scale image, based on a determination result by the correlation degree determination device; and an object type determination device that determines a type of the object based on the height of the binarized object calculated by the height calculation device.