A method for detecting lane elements, which are unit regions including pixels of lanes in an input image, to plan the drive path of an autonomous vehicle by using a horizontal filter mask is provided. The method includes steps of: a computing device acquiring a segmentation score map from a CNN using the input image; instructing a post-processing module, capable of performing data processing at an output end of the CNN, to generate a magnitude map by using the segmentation score map and the horizontal filter mask; instructing the post-processing module to determine each of lane element candidates per each of rows of the segmentation score map by referring to values of the magnitude map; and instructing the post-processing module to apply estimation operations to each of the lane element candidates per each of the rows, to thereby detect each of the lane elements.