An image forming apparatus includes an image bearing member and a developing device for developing an electrostatic latent image. The developing device includes a developer container, a rotatable developer carrying member, including a first electrode member; and a developer supplying member, including a second electrode member. The apparatus further includes a measuring device capable of measuring a remaining developer amount; and a replenishing device for performing a replenishing operation by rotating the developer supplying member while applying a DC bias between the first and second electrode members 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 a polarity identical to a normal charge polarity of the developer. When the remaining developer amount measured is not more than a threshold, the replenishing operation is performed and the remaining developer amount is measured again.