A control device includes a toner-density-related value identifying unit, a supply-amount-related value identifying unit, and a correcting unit. The toner-density-related value identifying unit identifies a toner-density-related value indicating the ratio of toner in developer including toner and carrier and contained in a developing unit that contains and agitates the developer. The supply-amount-related value identifying unit identifies the supply-amount-related value of developer to the developing unit. The correcting unit corrects the toner-density-related value identified by the toner-density-related value identifying unit in accordance with the supply-amount-related value identified by the supply-amount-related value identifying unit. The supply-amount-related value identifying unit estimates the supply-amount-related value on the basis of the consumption-amount-related value of developer.