A developing apparatus usable with an image forming apparatus, comprising: a developer cartridge having an outlet through which developer is discharged out of the developer cartridge; a developing cartridge in which the developer cartridge is detachably disposed, the developing cartridge having an inlet through which the developer discharged from the outlet of the developer cartridge enters into the developing cartridge; and a connecting member connecting the outlet of the developer cartridge and the inlet of the developing cartridge so as to allow the developer to be supplied from the developer cartridge to the developing cartridge, wherein a height of the connecting member is smaller than a maximum width of the inlet of the developing cartridge, wherein the developer cartridge includes a developer-conveying member configured to move developer in the developer cartridge toward the outlet, wherein the developer conveying member comprises: a conveying portion to convey the developer in a first direction toward the outlet; and a backflow portion configured to allow the developer to move in a second direction opposite to the first direction according to pressures at the outlet of the developer cartridge and the inlet of the developing cartridge, wherein the developer conveying member is configured to move the developer in the first direction when an outlet pressure at the outlet of the developer cartridge is larger than an inlet pressure at the inlet of the developing cartridge, and to allow a movement of the developer in the second direction when the outlet pressure at the outlet of the developer cartridge is smaller than the inlet pressure at the inlet of the developing cartridge; characterized in that the developer cartridge comprises a developer receiving portion including a first portion in which the outlet is formed and a second portion, a bottom surface of which is lower than a bottom surface of the first portion; and wherein the developer conveying member is formed as a hollow helical screw having a small diameter portion corresponding to the bottom surface of the first portion of the developer receiving portion and a large diameter portion corresponding to the bottom surface of the second portion of the developer receiving portion. a developer cartridge having an outlet through which developer is discharged out of the developer cartridge; a developing cartridge in which the developer cartridge is detachably disposed, the developing cartridge having an inlet through which the developer discharged from the outlet of the developer cartridge enters into the developing cartridge; and a connecting member connecting the outlet of the developer cartridge and the inlet of the developing cartridge so as to allow the developer to be supplied from the developer cartridge to the developing cartridge, wherein a height of the connecting member is smaller than a maximum width of the inlet of the developing cartridge, wherein the developer cartridge includes a developer-conveying member configured to move developer in the developer cartridge toward the outlet, a conveying portion to convey the developer in a first direction toward the outlet; and a backflow portion configured to allow the developer to move in a second direction opposite to the first direction according to pressures at the outlet of the developer cartridge and the inlet of the developing cartridge,