An image processing apparatus comprising: an image acquisition unit; a tilt information calculator that calculates a plurality of pieces of edge information, including an angle or direction of the edge, in an image acquired by the image acquisition unit in order to estimate a tilt of the image; a tilt information-position recording unit that records correspondences between the plurality of pieces of edge information and positions in the image in which the plurality of pieces of edge information are acquired; characterized by an angle histogram generator that generates an angle histogram, which is a frequency distribution of each tilt angle, using the plurality of pieces of edge information calculated by the tilt information calculator; a tilt information distribution degree calculator that calculates a distribution degree of the tilt information from the plurality of pieces of edge information and the positions of the plurality of pieces of edge information; wherein the distribution degree is calculated based on position information corresponding to sets of tilt information having identical tilt angles or similar tilt angles existing in a predetermined angle range; a fake information determination unit that determines the tilt information that can be used in tilt estimation and the tilt information that cannot be used in the tilt estimation in the plurality of pieces of edge information from the distribution degree of the tilt information; wherein a small distribution degree indicates that the corresponding tilt information cannot be used; a peak detector that extracts a maximum value or a maximum of the usable angle histogram based on a determination result of the fake information determination unit; and a tilt estimation unit that estimates the tilt angle of the image from the tilt angle indicated by the maximum value or the maximum, which is detected by the peak detector. an image acquisition unit; a tilt information calculator that calculates a plurality of pieces of edge information, including an angle or direction of the edge, in an image acquired by the image acquisition unit in order to estimate a tilt of the image; a tilt information-position recording unit that records correspondences between the plurality of pieces of edge information and positions in the image in which the plurality of pieces of edge information are acquired; characterized by an angle histogram generator that generates an angle histogram, which is a frequency distribution of each tilt angle, using the plurality of pieces of edge information calculated by the tilt information calculator; a tilt information distribution degree calculator that calculates a distribution degree of the tilt information from the plurality of pieces of edge information and the positions of the plurality of pieces of edge information; wherein the distribution degree is calculated based on position information corresponding to sets of tilt information having identical tilt angles or similar tilt angles existing in a predetermined angle range; a fake information determination unit that determines the tilt information that can be used in tilt estimation and the tilt information that cannot be used in the tilt estimation in the plurality of pieces of edge information from the distribution degree of the tilt information; wherein a small distribution degree indicates that the corresponding tilt information cannot be used; a peak detector that extracts a maximum value or a maximum of the usable angle histogram based on a determination result of the fake information determination unit; and a tilt estimation unit that estimates the tilt angle of the image from the tilt angle indicated by the maximum value or the maximum, which is detected by the peak detector.