A three-dimensional object detection device comprising: an image capturing unit mounted in a vehicle and provided with a lens and an image capturing element, the image capturing means being configured to form a video image of a predetermined area (A1, A2); a viewpoint conversion unit configured to convert the viewpoint of an image obtained by the image capturing means into a bird's-eye view image (PB t, PB t-1); a three-dimensional object detection unit (33, 37) configured to align, in a bird's-eye view, the positions of bird's-eye view images (PB t, PB t-1) from different points in time obtained by the viewpoint conversion unit, generate differential waveform information by forming a frequency distribution upon counting, in a differential image of the aligned bird's-eye view images (PB t, PB t-1), the number of pixels indicating a predetermined difference in the differential image along the direction of collapsing of the three-dimensional object corresponding to lines extending vertically in real space when viewpoint conversion of the bird's-eye view image (PB t, PB t-1) has been performed, and detect a three-dimensional object based on the differential waveform information; and a three-dimensional object assessment unit configured to assess whether or not a three-dimensional object detected by the three-dimensional object detection means (33, 37) is another vehicle, characterized by further comprising: a first foreign matter detection unit configured to detect whether or not foreign matter has adhered to the lens based on the change over time in the luminance values for each predetermined pixel in the image capturing element; a second foreign matter detection unit configured to extract a first maximum from differential waveform information generated at one or a plurality of first timings by the three-dimensional object detection means (33, 37), acquire a reference value based on the extracted first maximum, extract a second maximum at the same position than the first maximum in the bird's-eye view image (PB t, PB t-1) from differential waveform information newly generated at one or a plurality of second timings after the first timings, acquire an evaluation value based on the second maximum, and detect whether or not foreign matter has adhered to the lens based on the change over time in the difference between the evaluation value and the reference value; and a controller that, when the first foreign matter detection unit and the second foreign matter detection unit have detected foreign matter that has adhered to the lens, is configured to suppress the detection of the three-dimensional object from an image of the predetermined area (A1, A2) and the assessment that the three-dimensional object is the other vehicle. an image capturing unit mounted in a vehicle and provided with a lens and an image capturing element, the image capturing means being configured to form a video image of a predetermined area (A1, A2); a viewpoint conversion unit configured to convert the viewpoint of an image obtained by the image capturing means into a bird's-eye view image (PB t, PB t-1); a three-dimensional object detection unit (33, 37) configured to align, in a bird's-eye view, the positions of bird's-eye view images (PB t, PB t-1) from different points in time obtained by the viewpoint conversion unit, generate differential waveform information by forming a frequency distribution upon counting, in a differential image of the aligned bird's-eye view images (PB t, PB t-1), the number of pixels indicating a predetermined difference in the differential image along the direction of collapsing of the three-dimensional object corresponding to lines extending vertically in real space when viewpoint conversion of the bird's-eye view image (PB t, PB t-1) has been performed, and detect a three-dimensional object based on the differential waveform information; and a three-dimensional object assessment unit configured to assess whether or not a three-dimensional object detected by the three-dimensional object detection means (33, 37) is another vehicle, a first foreign matter detection unit configured to detect whether or not foreign matter has adhered to the lens based on the change over time in the luminance values for each predetermined pixel in the image capturing element; a second foreign matter detection unit configured to extract a first maximum from differential waveform information generated at one or a plurality of first timings by the three-dimensional object detection means (33, 37), acquire a reference value based on the extracted first maximum, extract a second maximum at the same position than the first maximum in the bird's-eye view image (PB t, PB t-1) from differential waveform information newly generated at one or a plurality of second timings after the first timings, acquire an evaluation value based on the second maximum, and detect whether or not foreign matter has adhered to the lens based on the change over time in the difference between the evaluation value and the reference value; and a controller that, when the first foreign matter detection unit and the second foreign matter detection unit have detected foreign matter that has adhered to the lens, is configured to suppress the detection of the three-dimensional object from an image of the predetermined area (A1, A2) and the assessment that the three-dimensional object is the other vehicle.