Patent ID: 8488984

Claim:
An image forming apparatus comprising: a developing device; a toner supply device; a toner supply detecting sensor; and, a toner concentration controller, wherein the developing device comprises: a developer container for storing a developer including a toner and a magnetic carrier; a developer conveying structure disposed inside the developer container for circulatively conveying the developer whilst agitating; a developing roller for supplying the toner included in the developer to a photoreceptor drum; and, a toner supply port that leads supplied toner into the developer container, the toner supply device supplies the toner into the developing device, the toner supply detecting sensor detects whether the toner has been supplied into the developer container, the toner concentration controller instructs the toner supply device to supply toner to the developing device when the toner concentration of the developer in the developing device has become lower than a predetermined reference concentration, the toner concentration controller determines that the toner in the toner supply device is empty when the toner supply detecting sensor has detected no toner supply after a command of toner supply was given, the toner concentration controller includes: a memory that stores either the difference, or the ratio, between the outputs from toner supply detecting sensor before and after toner supply from the toner supply device, as a toner supply quantity evaluation index; a toner supply quantity determinater that determines whether the toner supply quantity evaluation index is smaller than a predetermined supply reference value; and, an image quality adjustment controller that shortens the interval of time between adjustments of electrical potential for controlling the density of a toner image formed on the photoreceptor drum, when the toner supply quantity evaluation index is smaller than the supply reference value.