Image forming apparatus featuring a developer replenishing device

An image forming apparatus comprising:

• an image bearing member on which an electrostatic latent image is to be formed;
• a developing device for developing the electrostatic latent image by supplying a developer to said image bearing member, said developing device including:
• a developer container for containing the developer;
• a rotatable developer carrying member, including a first electrode member, for carrying and supplying the developer to said image bearing member;
• and
• a developer supplying member, which is provided in contact with said developer carrying member and includes a surface foam layer and a second electrode member for rotatably supporting said developer supplying member, for supplying the developer to said developer carrying member;
• a first measuring device for measuring a remaining developer amount in said developer container;
• a second measuring device capable of measuring the remaining developer amount by detecting electrostatic capacity between the first electrode member and the second electrode member;
• and
• a replenishing device for performing a replenishing operation for replenishing said developer supplying member with the developer by rotating said developer supplying member while applying a DC bias between the first electrode member and the second electrode member so that a value obtained by subtracting an electric potential of the second electrode member from an electric potential of the first electrode member has an identical polarity to a normal charge polarity of the developer,
• wherein when the remaining developer amount measured by said first measuring device is not more than a threshold, the replenishing operation is performed by said replenishing device and thereafter the remaining developer amount is measured by said second measuring device.