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 so as to clip the second diagnostic region.