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.