1. A lane detection method comprising: acquiring S 10 an image in front of a vehicle using a photographing unit provided in the vehicle; detecting S 20 , from the acquired image, a positive edge (P.E.) in which a right pixel has a higher brightness value than a brightness value of a left pixel; detecting S 30 , from the acquired image, a negative edge (N.E.) in which a left pixel has a higher brightness value than a brightness value of a right pixel; generating S 40 a first expansion image by expanding a pixel by a length corresponding to a width of a lane on a right side of the positive edge (P.E.); generating S 50 a second expansion image by expanding the pixel by the length corresponding to the width of a lane on a left side of the negative edge (N.E.); and detecting S 60 the lane by combining the first expansion image and the second expansion image.