An image decoloring device operates in a power-saving mode and in a normal mode. The image decoloring device includes a decoloring processing unit which removes a color of a decolorable colorant that forms an image on a sheet by applying heat to the sheet. A sheet carrying unit conveys the sheet through the decoloring processing unit. A processor controls the sheet carrying unit. If the image decoloring device is operating in the power-saving mode, a conveyance speed of the sheet through the decoloring processing unit is a first speed. If the image decoloring carrying unit is operating in the normal mode, the conveyance speed of the sheet through the decoloring processing unit is a second speed greater than the first speed.