A developing device develops an electrostatic latent image formed on an electrophotographic photosensitive member. The developing device is mountable to a main assembly of an electrophotographic image forming apparatus. The developing device includes a developer carrying member for feeding a developer to the electrophotographic photosensitive member to develop the electrostatic latent image formed on the electrophotographic photosensitive member, a first electroconductive portion, a second electroconductive portion for cooperating with the first electroconductive portion to provide an electrostatic capacity, a first electrical contact for receiving a voltage to be applied to the first electroconductive portion from the main assembly of the electrophotographic image forming apparatus, and a second electrical contact for transmitting, to the main assembly of the electrophotographic image forming apparatus, an electric signal corresponding to an electrostatic capacity between the first electroconductive portion and the second electroconductive portion when a voltage is applied to the first electroconductive portion to detect a remaining amount of the developer by the main assembly of the electrophotographic image forming apparatus.