An image processing portion determines that a black stripe is present when among a plurality of main scanning lines included in a back end side range from a last back end position of the reading image data in a sub-scanning direction to a predetermined position, a main scanning line in which a density value of a pixels in a predetermined position is higher than a first threshold density is present, sets, at a reference line, a main scanning line farthest from the last back end position among the main scanning lines in which the density value of the pixel in the predetermined position is higher than the first threshold density and replaces density values of all pixels included in a range from a position of the reference line in the sub-scanning direction to the last back end position with a density value corresponding to white.