A three-dimensional object detection device for detecting a three-dimensional object around a vehicle, the device comprising: an image capturing device configured to capture an image of an area diagonally behind the vehicle; a viewpoint conversion unit configured to perform viewpoint conversion processing of projecting the image captured by the image capturing device onto road surface to create a bird's eye view image; a luminance difference calculator configured to set a line segment extending in a vertical direction in an actual space as a first vertical imaginary line (L a ) in the bird's eye view image and a second vertical imaginary line (L r ) which is away from the first vertical imaginary line (L a ) by a predetermined distance in the actual space and which extends in the vertical direction in the actual space, set a pixel (P a,i ) for each of a plurality of positions along the first vertical imaginary line (L a ) and a pixel (P r.i ) for each of a plurality of positions along the second vertical imaginary line (Lr) in such a way that the pixel (P r,i ) and the pixel (P a,i ) are located respectively at almost the same heights in the actual space, and calculate a luminance difference between the two pixels (P a,i , P r,i ) set for each of the plurality of positions; an edge line detector configured to add an attribute to each of the positions on the first vertical imaginary line (L a ) on the basis of the luminance difference of the position on the first vertical imaginary line (L a ) and to detect an edge line on the basis of continuities of the attributes; and a three-dimensional object detector configured to detect the three-dimensional object on the basis of a quantity of the edge lines detected by the edge line detector . an image capturing device configured to capture an image of an area diagonally behind the vehicle; a viewpoint conversion unit configured to perform viewpoint conversion processing of projecting the image captured by the image capturing device onto road surface to create a bird's eye view image; a luminance difference calculator configured to set a line segment extending in a vertical direction in an actual space as a first vertical imaginary line (L a ) in the bird's eye view image and a second vertical imaginary line (L r ) which is away from the first vertical imaginary line (L a ) by a predetermined distance in the actual space and which extends in the vertical direction in the actual space, set a pixel (P a,i ) for each of a plurality of positions along the first vertical imaginary line (L a ) and a pixel (P r.i ) for each of a plurality of positions along the second vertical imaginary line (Lr) in such a way that the pixel (P r,i ) and the pixel (P a,i ) are located respectively at almost the same heights in the actual space, and calculate a luminance difference between the two pixels (P a,i , P r,i ) set for each of the plurality of positions; an edge line detector configured to add an attribute to each of the positions on the first vertical imaginary line (L a ) on the basis of the luminance difference of the position on the first vertical imaginary line (L a ) and to detect an edge line on the basis of continuities of the attributes; and a three-dimensional object detector configured to detect the three-dimensional object on the basis of a quantity of the edge lines detected by the edge line detector . <EOS>