A developer cartridge constructed in a structure in which an overload is not applied to stirring units to stir a developer even when the developer is lump includes a housing having a developer storage chamber, a first stirring unit rotatably mounted in the housing, and a second stirring unit rotatably mounted in the housing such that the second stirring unit is rotatable with time delay after a rotation of the first stirring unit. The second stirring unit includes a rotary shaft, and the developer cartridge further includes a rotary member coupled to one end of the rotary shaft and a power transmission member to transmit a rotary force to the rotary member after rotation thereof by a predetermined angle.