A developing device includes a storage portion storing a developer, a conveying portion stirring and conveying the developer in the storage portion, a sensor, an acquisition processing portion, and a correction processing portion. The sensor outputs an electrical signal in accordance with magnetic permeability at a predetermined detection position in a conveyance path of the developer. The acquisition processing portion acquires a specific value based on the electrical signal outputted during a rotation period of the conveying portion. The correction processing portion corrects the specific value based on a rotation speed of the conveying portion when a fluctuation width of the electrical signal outputted during the rotation period of the conveying portion is less than a predetermined threshold, and corrects the specific value based on the rotation speed of the conveying portion and the fluctuation width when the fluctuation width is equal to or greater than the threshold.