There is provided a decoloring device including a decoloring unit, a first sheet conveying unit, a first sheet feed unit, a thickness detecting unit, a decolorability determining unit, and a second sheet feed unit. The first sheet conveying unit conveys the sheet to the decoloring unit. The first sheet feed unit feeds the sheet to the first sheet conveying unit. The decolorability determining unit determines whether or not the sheet which is subject to thickness detecting is decolorable by the decoloring unit based on a detection result in the thickness detecting unit. A second sheet feed unit is disposed at a downstream side in relation to the thickness detecting unit and at an upstream side in relation to the decoloring unit in a sheet conveying path by the first sheet conveying unit and feeds the sheet to the first sheet conveying unit.