Image forming apparatus for determining remaining amount of developer in developer container

An image forming apparatus comprising a developing unit that contains developer and that is detachable, the image forming apparatus comprising:

• a rotation member that comprises a first electrode and that moves around a rotation shaft in the developing unit, the rotation member being provided on the rotation shaft having flexibility such that the rotation shaft is deformed by resistance of the developer;
• a second electrode that is provided at a position where the first electrode is not affected by the resistance of the developer even if the developer is full and that is provided near an outer surface of the developing unit;
• a third electrode that is provided at a position where the first electrode is affected by the resistance of the developer even if an amount of the developer is smaller than when the developer is full and that is provided near the outer surface of the developing unit;
• a detection unit that detects an electrostatic capacitance between the first electrode and the second electrode or between the first electrode and the third electrode;
• a measurement unit that measures a first time at which the detection unit has detected the electrostatic capacitance between the first electrode and the second electrode and a second time at which the detection unit has detected the electrostatic capacitance between the first electrode and the third electrode;
• and
• a determination unit that determines an amount of the developer based on a time difference between the first time and the second time measured by the measurement unit.