Image reading device, image reading device shading correction method, and image forming apparatus

An image reading device includes: a light source irradiating a reading target with light; an image sensor receiving incoming reflection light from the reading target and reading the reading target; a plurality of kinds of white reference plates of mutually different brightness levels provided for acquiring a white reference in shading correction; an input part accepting input of selection, as a mode for document reading, between a character mode prioritizing character reproduction and a photo mode prioritizing figure and photo reproduction; and a shading correction part, when the character mode has been selected, perform the shading correction by defining the white reference based on output of the image sensor when the character-mode white reference plate darker than the photo-mode white reference plate has been read.