A developing cartridge includes: 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 includes: a first gear part meshed with the developing roller driving gear; and a second gear part meshed with the supply roller driving gear. The driving force transmission gear transmits driving force to the developing roller driving gear and the supply roller driving gear.