A direction identification unit (21) identifies a traveling direction in which a surrounding vehicle travels in a partial region of a region indicated by image information (42) obtained by photographing using a camera (31). A feature amount acquisition unit (22) acquires a reference feature amount (41) being a feature amount computed from a reference image corresponding to the identified traveling direction. A vehicle determination unit (23) computes an image feature amount being a feature amount of the image information of the partial region and compares the computed image feature amount with the acquired reference feature amount (41), thereby determining whether the surrounding vehicle is present in the partial region.