1. A vehicle surroundings monitoring apparatus that extracts a body present in the surroundings 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 search region including a bottom end of the binarized object extracted by the binarized object extraction device, on the gray scale image; a horizontal edge detection device that detects a horizontal edge in the search region set by the search region setting device; a horizontal edge width calculation device that calculates a width of the horizontal edge detected by the horizontal edge detection device, or a status quantity related to the width; and an object type determination device that determines a type of the object based on the width of the horizontal edge or the status quantity related to the width calculated by the horizontal edge width calculation device.