First object candidate region extraction means extracts a first object candidate region where an object is expected to be present from an infrared light image captured by an infrared light imaging device. Second object candidate region extraction means extracts a second object candidate region where the object is expected to be present from a visible light image captured by a visible light imaging device. Score integration means calculates an integration evaluation value by performing a weighted addition of a first evaluation value in the first object candidate region and a second evaluation value in the second object candidate region. Weight decision means decides a weight in the weighted addition on the basis of, for example, an environment temperature. Object region determination means determines an object region on the basis of the integration evaluation value.