A sheet media reading control method includes conveying a sheet medium on which magnetic ink characters are printed through a transportation path, reading the magnetic ink characters and an image of the sheet medium using a magnetic head and an image sensor head positioned along the transportation path, extracting partial scanned image data containing at least an outside edge part of the sheet medium from the scanned image data captured by the image sensor head, executing a skew evaluation based on the partial scanned image data to detect if the sheet medium is conveyed skewed at a skew angle exceeding an allowable skew angle, and invalidating at least the magnetic ink character data captured by the magnetic head from sheet media that are determined by the skew evaluation to be skewed.