A developing unit includes: a developer carrier; a toner supplying member having a porous surface layer; a toner storage storing therein toner; a stirring member that is rotated to stir the toner; a toner amount detecting unit that detects an amount of the toner; a toner supplying unit that supplies new toner to the toner storage based on a detection result; and a toner removing member that removes the toner carried in the porous surface layer, wherein the toner removing member is arranged in a separable and contactable manner from and with the porous surface layer, and the developing unit has a stirring mode in which the toner removing member is brought into contact with the porous surface layer, and the toner supplying member is rotated while the stirring member is rotated to stir the toner.