A line segment detection method includes acquiring an image, extracting from the image a straight line that includes a line segment, acquiring a luminance distribution of the straight line, generating a virtual function model that contains a distribution of a foreground and a background of the image by using the luminance distribution, and determining whether luminance values near end points (start point and end point) of the line segment contained in the virtual function model probabilistically belong to the foreground or the background, and estimating end points (start point and end point) in the virtual function model.