A three-dimensional object detection device 1 includes a camera 10 and a calculator 20. The calculator 20 performs viewpoint conversion processing on an image captured by the camera 10 to create a bird's eye view image, calculates, for each of a plurality of positions along a vertical imaginary line extending in a vertical direction in an actual space, a luminance difference between two pixels near the position, and detects a three-dimensional object on the basis of continuities of the calculated luminance differences of the respective positions.