A developing cartridge that is detachably mountable to a main body of an image forming apparatus, the developing cartridge comprising: a developing roller that is rotatable about a developing roller axis line, which extends in a predetermined direction; a supply roller, which is rotatable about a supply roller axis line, which extends in the predetermined direction, and which supplies developer to the developing roller; a developing roller driving gear that is connected to the developing roller; a supply roller driving gear that is connected to the supply roller; and a driving force transmission gear, which is rotatable about a gear axis line extending in the predetermined direction, and which comprises: a first gear part meshed with the developing roller driving gear; and a second gear part meshed with the supply roller driving gear, wherein the driving force transmission gear transmits driving force to the developing roller driving gear and the supply roller driving gear, characterized in that the first gear part and the second gear part are each configured to generate thrust forces in directions that are opposite to each other, when the driving force transmission gear is rotated, and the first gear part is formed with a first helical tooth pattern and the second gear part is formed with a second helical tooth pattern, respectively, wherein the first helical tooth pattern and the second helical tooth pattern have tooth traces that follow helix pitches having directions different from each other, and wherein the driving force transmission gear further comprises a connection part, to which a main body-side driving member for inputting driving force is to be connected. a developing roller that is rotatable about a developing roller axis line, which extends in a predetermined direction; a supply roller, which is rotatable about a supply roller axis line, which extends in the predetermined direction, and which supplies developer to the developing roller; a developing roller driving gear that is connected to the developing roller; a supply roller driving gear that is connected to the supply roller; and a driving force transmission gear, which is rotatable about a gear axis line extending in the predetermined direction, and which comprises: a first gear part meshed with the developing roller driving gear; and a second gear part meshed with the supply roller driving gear, a first gear part meshed with the developing roller driving gear; and a second gear part meshed with the supply roller driving gear, wherein the driving force transmission gear transmits driving force to the developing roller driving gear and the supply roller driving gear, characterized in that the first gear part and the second gear part are each configured to generate thrust forces in directions that are opposite to each other, when the driving force transmission gear is rotated, and the first gear part is formed with a first helical tooth pattern and the second gear part is formed with a second helical tooth pattern, respectively, wherein the first helical tooth pattern and the second helical tooth pattern have tooth traces that follow helix pitches having directions different from each other, and wherein the driving force transmission gear further comprises a connection part, to which a main body-side driving member for inputting driving force is to be connected.