An image forming apparatus comprising: a developing device including a container that has an opening and contains a toner, a toner bearing member arranged at the opening of the container, having a first electrode member, and supplying an electrostatic latent image with the toner by bearing and conveying the toner, and a toner supply member arranged in the container and having a second electrode member and a foam layer, the foam layer being provided around the second electrode member, wherein the developing device supplies the toner bearing member with the toner in the container by rotating the toner supply member in a contact manner with the toner bearing member; a detection mode execution unit configured to execute a detection mode to detect a capacitance C 1 between the first and second electrode members, then rotate the toner supply member for changing a toner amount in the foam layer after the capacitance C 1 is detected, and then detect a capacitance C 2 between the first and second electrode members after the toner supply member is rotated; and a notice signal generating unit configured to generate a notice signal if an absolute value |C 1 - C 2 | of a difference between the capacitances C 1 and C 2 is smaller than a predetermined threshold, the notice signal being indicative of that a toner amount in the container is smaller than a predetermined amount. a developing device including a container that has an opening and contains a toner, a toner bearing member arranged at the opening of the container, having a first electrode member, and supplying an electrostatic latent image with the toner by bearing and conveying the toner, and a toner supply member arranged in the container and having a second electrode member and a foam layer, the foam layer being provided around the second electrode member, wherein the developing device supplies the toner bearing member with the toner in the container by rotating the toner supply member in a contact manner with the toner bearing member; a container that has an opening and contains a toner, a toner bearing member arranged at the opening of the container, having a first electrode member, and supplying an electrostatic latent image with the toner by bearing and conveying the toner, and a toner supply member arranged in the container and having a second electrode member and a foam layer, the foam layer being provided around the second electrode member, wherein the developing device supplies the toner bearing member with the toner in the container by rotating the toner supply member in a contact manner with the toner bearing member; a detection mode execution unit configured to execute a detection mode to detect a capacitance C 1 between the first and second electrode members, then rotate the toner supply member for changing a toner amount in the foam layer after the capacitance C 1 is detected, and then detect a capacitance C 2 between the first and second electrode members after the toner supply member is rotated; and a notice signal generating unit configured to generate a notice signal if an absolute value |C 1 - C 2 | of a difference between the capacitances C 1 and C 2 is smaller than a predetermined threshold, the notice signal being indicative of that a toner amount in the container is smaller than a predetermined amount.