1. A boundary line recognizer device, comprising: a camera mounted on a vehicle and capturing an image of a lane; an edge point extraction section extracting edge points on the basis of luminance of the image captured by the camera; a candidate line extraction section extracting a candidate line for a boundary line separating the lane on the basis of a succession of the extracted edge points; a frequency calculator section calculating, on the basis of the edge points on the candidate line extracted by the candidate line extraction section, a frequency distribution of the edge points relative to a parameter for specifying a width of the boundary line; and a probability generation section generating a probability distribution of the candidate line being the boundary line relative to the parameter on the basis of the frequency distribution calculated by the frequency calculator section; and a boundary line recognizer section recognizing the boundary line on the basis of the probability distribution generated by the probability generation section.