Provided is a tilt angle correction apparatus including a deriving unit that based on pixel values of plural pixels corresponding to a predetermined side of an original document of image information obtained by reading the original document, derives a tilt angle of the side relative to a predetermined reference and derives a degree of reliability of the derived tilt angle, and a correction unit that corrects a direction of an image shown by the image information, based on the derived tilt angle when the degree of reliability is over a predetermined threshold.