Speed detection device, speed detection method, speed detection program, and recording medium

An imaging unit (210A) is controlled while a relative speed output unit (113A) performs control for alternately switching, via an illumination switching unit (112) at each predetermined time, illumination by a plurality of illumination units (120A 1 , 120A 2 ) for illuminating a road surface at mutually different angles, and an image of the road surface is captured. Then, the relative speed output unit (113A) determines the illumination unit that corresponds to a captured image for calculating speed information of a moving body (MV) on the basis of the captured image from the imaging unit (210A) obtained via an acquisition unit (111A). The relative speed output unit (113A) then calculates relative sped information (VLI) of each time point on the basis of the captured image at the time of illumination by the determined illumination unit and outputs the calculated relative speed information (VLI). As a result, relative speed information can be calculated with good precision and outputted even when the state of the road surface changes moment by moment.