An image forming apparatus (1), which is used to perform a method of reading images, includes an image reading device (120) and an image forming device (4) to form an image on a recording medium (P). The image reading device (120) includes an image reading body (36) configured to read one of a recording medium (P) and the recording medium (P) together with a background area adjacent to the recording medium (P), a moving body (123) disposed facing the image reading body (36), and a reference body (100) as a reference in shading correction. The moving body (123) is configured to hold the recording medium (P) and the reference body (100) in a direction intersecting a sheet conveying direction of the recording medium (P) such that the recording medium (P) and the reference body (100) contact to and separate from the image reading body (36).