A vehicle environment monitoring device identifies objects from an image taken by an infrared camera. Object extraction from images is performed in accordance with the state of the environment as determined by measurements extracted from the images as follows: N1 binarized objects are extracted from a single frame. Height of a grayscale objects corresponding to one of the binarized objects are calculated. If a ratio of the number of binarized objects C, where the absolute value of the height difference is less than the predetermined value .DELTA.H, to the total number N1 of binarized objects, is greater than a predetermined value X1, the image frame is determined to be rainfall-affected. If the ratio is less than the predetermined value X1, the image frame is determined to be a normal frame. A warning is provided if it is determined that the object is a pedestrian and if a collision is likely.