An image forming apparatus includes a developing device, a detection mode execution unit, and a notice signal generating unit. The developing device supplies a toner bearing member with toner in a container by rotating a toner supply member in a contact manner with the toner bearing member. The detection mode execution unit executes a detection mode in which a predetermined period for changing a toner amount in the foam layer by rotating the toner supply member is provided, a capacitance C1 between the first and second electrode members is detected before the predetermined period, and a capacitance C2 between the first and second electrode members is detected after the predetermined period. The notice signal generating unit generates a low toner amount notice signal in response to an absolute value |C1−C2| of a difference between the capacitances C1 and C2 being smaller than a predetermined threshold.