A processing device, a sheet manufacturing apparatus, a processing method, and a sheet manufacturing method that suppress damage to a substrate when removing color material from the substrate, and are useful for recycling the substrate after color material is removed, are provided. A processing device has a color material removal device including at least one discharge nozzle configured to discharge particles containing cellulose to a substrate holding color material, and remove the color material from the substrate. The color material removal device preferably has a double-walled conduit construction having an internal conduit and an external conduit in which the internal conduit is inserted, at least one of an opening to the internal conduit and an opening to the external conduit functioning as the discharge nozzle.