The present invention provides a technique capable of obtaining image data without a missing part even in a case where a business form is not rectangular. An image reading device including a reading unit which reads an image of a business form, the image reading device includes a skew angle calculation unit which calculates a skew angle used for correcting inclination of the business form according to image data of the image read by the reading unit, a circumscribed region detection unit which generates an image after a first skew correction obtained by rotating the image according to the skew angle, scans the generated image after the first skew correction, and thus detects a circumscribed quadrangle circumscribed around the image of the business form and included in the image after the first skew correction, and an image cutout unit which cuts out a business-form image after cutout from the image read by the reading unit, according to coordinates of four corner points of the circumscribed quadrangle.