1. An image processing apparatus for applying trimming processing to a radiographic image acquired by an imaging apparatus for acquiring the radiographic image of a subject, the image processing apparatus comprising: an image rotation unit for rotating the radiographic image so that the subject is aligned with a given direction to produce a display image; a diagnostic region designation unit for designating a first diagnostic region to be clipped with a diagnostic region designation frame represented by a rectangle for the display image; and a trimming processing unit for calculating a second diagnostic region in the radiographic image from a rotation amount of the display image and diagnostic region information representing the first diagnostic region and applying the trimming processing to the radiographic image to clip the second diagnostic region.