Bicycles present before a vehicle are identified. A picked-up image having intensity values that are in accordance with the temperatures of objects is acquired to extract image regions having intensity values representative of higher temperatures than a background. An object, which includes a pair of first object portions (legs) and a second object portion (a tire), would be identified as a bicycle if the pair of first object portions, which have greater dimensions in length in the vertical direction than in width in the horizontal direction and the distance between which is less than a predetermined value in the horizontal direction, are detected from the extracted image regions and further if the second object portion, which has a different intensity value from any one of the first object portions and also has a length greater than a predetermined value in the vertical direction, is existent between the pair of first object portions.