A developer cartridge comprising: a housing configured to accommodate developer therein; a first gear rotatable about a first axis extending in an axial direction, the first gear comprising: a small-diameter gear portion; and a large-diameter gear portion having a diameter larger than a diameter of the small-diameter gear portion; and a second gear rotatable about a second axis extending in the axial direction, the second gear comprising: a first columnar portion extending in the axial direction and centered on the second axis; a second columnar portion extending in the axial direction and centered on the second axis, the second columnar portion having a diameter smaller than a diameter of the first columnar portion; and a first engagement portion extending along a portion of a peripheral surface of the first columnar portion, characterized in that the first engagement portion is engageable with the small-diameter gear portion, and the second gear further comprises: a second engagement portion extending along a portion of a peripheral surface of the second columnar portion, the second engagement portion being positioned closer to the housing than the first engagement portion to the housing in the axial direction, the second engagement portion being engageable with the large-diameter gear portion; and a protrusion protruding in the axial direction, the protrusion being rotatable together with the first engagement portion and the second engagement portion, wherein the second engagement portion is configured to engage the large-diameter gear portion after the first engagement portion is engaged with the small-diameter gear portion. a housing configured to accommodate developer therein; a first gear rotatable about a first axis extending in an axial direction, the first gear comprising: a small-diameter gear portion; and a large-diameter gear portion having a diameter larger than a diameter of the small-diameter gear portion; and a small-diameter gear portion; and a large-diameter gear portion having a diameter larger than a diameter of the small-diameter gear portion; and a second gear rotatable about a second axis extending in the axial direction, the second gear comprising: a first columnar portion extending in the axial direction and centered on the second axis; a second columnar portion extending in the axial direction and centered on the second axis, the second columnar portion having a diameter smaller than a diameter of the first columnar portion; and a first engagement portion extending along a portion of a peripheral surface of the first columnar portion, a first columnar portion extending in the axial direction and centered on the second axis; a second columnar portion extending in the axial direction and centered on the second axis, the second columnar portion having a diameter smaller than a diameter of the first columnar portion; and a first engagement portion extending along a portion of a peripheral surface of the first columnar portion, characterized in that the first engagement portion is engageable with the small-diameter gear portion, and the second gear further comprises: a second engagement portion extending along a portion of a peripheral surface of the second columnar portion, the second engagement portion being positioned closer to the housing than the first engagement portion to the housing in the axial direction, the second engagement portion being engageable with the large-diameter gear portion; and a protrusion protruding in the axial direction, the protrusion being rotatable together with the first engagement portion and the second engagement portion, a second engagement portion extending along a portion of a peripheral surface of the second columnar portion, the second engagement portion being positioned closer to the housing than the first engagement portion to the housing in the axial direction, the second engagement portion being engageable with the large-diameter gear portion; and a protrusion protruding in the axial direction, the protrusion being rotatable together with the first engagement portion and the second engagement portion, wherein the second engagement portion is configured to engage the large-diameter gear portion after the first engagement portion is engaged with the small-diameter gear portion.