1. An in-vehicle device detecting and judging a three-dimensional object on a boundary of a road on which a vehicle runs, the device comprising: an image acquisition section having two or more cameras for image-capturing the road area; a distance data acquisition section acquiring three-dimensional distance information about an image-capture area on the basis of an image obtained by the image acquisition section; a road boundary detection section detecting the height of a three-dimensional object existing in the road area on the basis of the three-dimensional distance information obtained by the distance data acquisition section to detect a road boundary; and a same boundary judgment section transforming the image, for a first road area where the height of a three-dimensional object corresponding to a road boundary could be detected by the road boundary detection section and a second road area where the height of a three-dimensional object corresponding to a road boundary could not be detected by the road boundary detection section, and judging whether the three-dimensional object corresponding to the first road area and the three-dimensional object corresponding to the second road area are the same; wherein if the same boundary judgment section judges that the three-dimensional objects corresponding to the first and second road area boundaries are the same, the second road area is reset as the first road area.