An image reading device includes an image reading section, an image processing section, and a density reference member. Based on a location of a defect in the image reading section or in the density reference member, the image processing section determines whether or not to at least partially restrict either a read range of the image reading section when the image reading section reads an original document or usage of a result obtained by reading the original document by the image reading section. The image processing section determines whether or not to apply a smoothing process to each density value detected by reading the original document by the image reading section. The determination is made based on a comparison between a normal-value determining threshold and each density value detected by reading the density reference member by the image reading section.