A developing device includes a supplying chamber, an agitating member, a toner carrier, a retaining part and a detecting part. The supplying chamber accommodates a toner replenished from a toner container. The agitating member agitates the toner in the supplying chamber. The toner carrier supplies an electrostatic latent image formed on an image carrier with the toner from the supplying chamber. The retaining part recovers and retains the toner dispersed in the vicinity of the image carrier and the toner carrier. The detecting part detects an amount of the toner in the retaining part. The retaining part is moreover configured to replenish the recovered toner from the retaining part to the supplying chamber when the detecting part detects an amount of the toner in the retaining part more than a predetermined amount in a state where the toner is needed to be replenished to the supplying chamber.