To provide a two-component developing apparatus of an image forming apparatus which selectively discharges degraded carriers generated in a trickle development, using a two-component developer.

A second agitating/carrying screw 6 is arranged in a second chamber 11 to perform "replenishing", "returning and receiving", "mixing and stirring", "partially discharging" and "feeding to a developing unit" of the two-component developer 15. In the second agitating/carrying screw, the screw shaft 12 thereof is made of a magnetic material and is fixed on a case 2; the fin 13 thereof is made of a non-magnetic material and rotates along the periphery of the screw shaft 12, thereby stirring and carrying the two-component developer 15 in the direction of an arrow (g) as a whole. A new carrier 19a, having high electrostatic chargeability, is strongly attracted by the magnetic force of the screw shaft 12, is carried in the direction of the arrow (g), together with a toner and is fed to the developing unit, and the degraded carrier 19b having low electrostatic chargeability is peeled off from the screw shaft 12 by the fin 13 or is blown centrifugally and is separated down below, is carried in the direction of the arrow (g) together with the toner and is discharged from a discharge port.