A developer cartridge including a housing, a spring auger, and a rotation member. The housing accommodating a developer and including a first end portion and a second end portion in a lengthwise direction. The housing is to discharge the developer through a developer discharge outlet coupled to the housing and adjacent to one of the first end portion and the second end portion. The spring auger is located inside the housing and is to rotate to transport the developer to the developer discharge outlet. The rotation member is located at the first end portion of the housing and connected to a first end of the spring auger to rotate the spring auger. A first portion of a bottom surface of the housing is flat and a second portion of the bottom surface is internally convex from the first portion are repeatedly arranged on the bottom surface in the lengthwise direction.