1. A vehicle surroundings monitoring apparatus which monitors the surroundings of a vehicle by using an image captured by a camera mounted on the vehicle, comprising: a first image portion extraction process unit which extracts a first image portion likely to be an image of a first predetermined portion in a predetermined type of object in a real space from the captured image; a reference mask area setting process unit which sets a predetermined area including the first image portion as a reference mask area in the captured image; a lower search area setting process unit which sets a lower search area under the reference mask area in the captured image; a second image portion search process unit which searches for a second image portion having a preset feature value corresponding to a second predetermined portion in the predetermined type of object within the lower search area; and an object type determination process unit which determines the type of object in the real space corresponding to the first image portion according to whether the second image portion search process unit detects a plurality of the second image portions.