An image reading device includes: an area sensor in which color filters of three colors of R, G, and B are arranged in a Bayer array and a light receiving amount is detected by a light receiving element for each color filter; and a hardware processor that: reads a document by using the light receiving elements in a first group in the area sensor, reads the document by using the light receiving elements in a second group in the area sensor, at a region shifted by ½ pixels in a sub-scanning direction from a reading region of the light receiving elements in the first group, and interpolates R-color read data and B-color read data using G-color read data and synthesizes image data having a resolution twice the resolution of the area sensor.