To reduce the amount of discharged developer by separating and discharging only deteriorated developer whose electrification ability is dropped.

A developer separating device and an image forming apparatus have a circulation stirring chamber (6+7) having a first stirring chamber (6) and a second stirring chamber (7), which are partitioned by a partition wall (9), a developing container (V) having a developer replenishment port replenishing developer and a developer discharge port discharging developer, a developing unit (Gk) having a first stirring member (R1) and a second stirring member (R2), which transport developer in opposite directions while it is stirred, and an electric field curtain generation member (11) generating an electric field curtain separating developer having much electrification quantity and developer with less electrification quantity by transporting developer with much electrification quantity to the other stirring chamber (7) and preventing developer with less electrification quantity from being transported among transported developer.