An image inspector comprising: a reading device configured to read an image on a recording medium; and a control unit configured to determine whether the recording medium has a wrinkle and an edge folding based on a plurality of positions on the image on the recording medium read by the reading device satisfying a first predetermined relation and a second predetermined relation, the control unit being configured to: set the measurement positions of feature points {x0, y0}, {x1, y1}, {x2,y2} and{x3, y3}; determine whether the recording medium has the wrinkle based on the first predetermined relation; and then determine whether the recording medium has the edge folding based on the second predetermined relation, wherein the first predetermined relation is satisfied when the expression of D1 ≠ D2 is satisfied, and wherein the second predetermined relation is satisfied when the expression of (x2 - x0): (x3 - x1) ≠ (y0 - y2): (y1 - y3) is satisfied, wherein D1 and D2 are distances calculated between two sides facing each other along the conveyance direction of the sheet P at different positions, such that two lines of length D1 and D2 between the two sides are parallel with each other, and wherein the feature points of {x0, y0}, {x1, y1}, {x2,y2} and{x3, y3}; are set for determining sheet edge folding. a reading device configured to read an image on a recording medium; and a control unit configured to determine whether the recording medium has a wrinkle and an edge folding based on a plurality of positions on the image on the recording medium read by the reading device satisfying a first predetermined relation and a second predetermined relation, the control unit being configured to: set the measurement positions of feature points {x0, y0}, {x1, y1}, {x2,y2} and{x3, y3}; determine whether the recording medium has the wrinkle based on the first predetermined relation; and then determine whether the recording medium has the edge folding based on the second predetermined relation, wherein the first predetermined relation is satisfied when the expression of D1 ≠ D2 is satisfied, and wherein the second predetermined relation is satisfied when the expression of (x2 - x0): (x3 - x1) ≠ (y0 - y2): (y1 - y3) is satisfied, wherein D1 and D2 are distances calculated between two sides facing each other along the conveyance direction of the sheet P at different positions, such that two lines of length D1 and D2 between the two sides are parallel with each other, and wherein the feature points of {x0, y0}, {x1, y1}, {x2,y2} and{x3, y3}; are set for determining sheet edge folding. set the measurement positions of feature points {x0, y0}, {x1, y1}, {x2,y2} and{x3, y3}; determine whether the recording medium has the wrinkle based on the first predetermined relation; and then determine whether the recording medium has the edge folding based on the second predetermined relation, wherein the first predetermined relation is satisfied when the expression of D1 ≠ D2 is satisfied, and wherein the second predetermined relation is satisfied when the expression of (x2 - x0): (x3 - x1) ≠ (y0 - y2): (y1 - y3) is satisfied, wherein D1 and D2 are distances calculated between two sides facing each other along the conveyance direction of the sheet P at different positions, such that two lines of length D1 and D2 between the two sides are parallel with each other, and wherein the feature points of {x0, y0}, {x1, y1}, {x2,y2} and{x3, y3}; are set for determining sheet edge folding.