Abstract: In a developing device, process cartridge, and the like, including a developer amount detector for detecting a developer amount by detecting a change in capacitance among a plurality of electrodes, a developer is circulated and supplied in an optimal manner among the electrodes constituting the developer amount detector. The lower end portion on the upper side of an opening is above the lower end portion of a second electrode. With the opening formed in this manner, when toner in a developer frame is fed into among the electrodes by a toner feeding member, the toner is urged into the developing frame without being interfered with by the lower end portion on the upper side of the opening. Ideal toner circulation and toner supply can be performed, and a detection error can be decreased.