1. A three-dimensional object detection device comprising: an image capturing unit configured to capture images of an area including a right-side detection area or a left-side detection area rearward of a vehicle; a three-dimensional object detection unit programmed to detect a three-dimensional object based on the images acquired by the image capturing unit; a high-luminance area assessment unit programmed to assess whether one of the right-side detection area and the left-side detection area includes a high-luminance area complying with a predetermined reference, and—if one of the right-side detection area and the left-side detection area includes the high-luminance area—to selectively designate the one of the right-side detection area and the left-side detection area as a first detection area and the other of the right-side detection area and the left-side detection area as a second detection area, the high-luminance area corresponding to a bright environment illuminated by light; and a controller programmed to selectively suppress detection of the three-dimensional object based on image information of the first detection area, and to maintain or promote detection of the three-dimensional object based on image information of the second detection area.