There is provided a decoloring device including a decoloring unit, a first sheet conveying unit, a pre-decoloring reading unit, a type determining unit, a second sheet conveying unit, a post-decoloring reading unit, a decoloring success or failure determining unit, and a determination criterion setting unit. The type determining unit determines the type of image on the sheet conveyed to the decoloring unit based on the reading result in the pre-decoloring reading unit. The post-decoloring reading unit reads an image on the sheet after the decoloring, which is conveyed by the second sheet conveying unit. The decoloring success or failure determining unit determines whether or not the decoloring in the decoloring unit is successful based on the reading result in the post-decoloring reading unit. The determination criterion setting unit sets a determination criterion in the decoloring success or failure determining unit, based on the type of image, which is determined by the type determining unit.