1. A lane detection method comprising: acquiring an image in front of a vehicle using a photographing device provided in the vehicle; detecting, from the acquired image, a positive edge (P.E.) a lane in which a right pixel has a higher brightness value than a brightness value of a left pixel; detecting, from the acquired image, a negative edge (N.E.) of the lane in which a left pixel has a higher brightness value than a brightness value of a right pixel; calculating the number of pixels corresponding to a width of the lane; generating a first expansion image of the lane by expanding a pixel from the P.E. by a length corresponding to the calculated number of pixels on a right side of the P.E., so that the first expansion image has the width of the lane; generating a second expansion image of the lane by expanding a pixel from the N.E. by the length corresponding to the calculated number of pixels on a left side of the N.E., so that the second expansion image has the width of the lane; and detecting the lane by performing an AND operation from the first expansion image and the second expansion image.