Developing apparatus

A cartridge detachably mounted to an apparatus main body of an image forming apparatus, the cartridge comprising:

• a developing unit including:
• a developing roller configured to be rotatable and supply toner to a photosensitive drum;
• a toner supply roller configured to supply the toner to the developing roller, the toner supply roller having a shaft rotatable about a rotational axis and an elastic portion formed outside the shaft, the elastic portion contacting with the developing roller;
• a coupling member configured to receive a driving force from the apparatus main body, the coupling member being provided on a side of a first end portion of the developing unit in a direction of the rotational axis;
• and
• a gear provided with a hole into which an end portion of the shaft is fitted, the end portion of the shaft being on a side of a second end portion of the developing unit opposite to the first end portion of the developing unit in the direction of the rotational axis, the gear being configured to be rotated by the driving force transmitted from the coupling member,
• wherein the end portion of the shaft has an outer peripheral surface including an outer circumferential surface and an outer flat surface adjacent to the outer circumferential surface in a rotational direction of the shaft,
• wherein the hole of the gear is constituted by an inner peripheral surface including first and second surfaces, the first surface being an inner circumferential surface facing the outer circumferential surface of the shaft, a second surface facing the outer flat surface of the shaft, and wherein when viewed in the direction of the rotational axis, the second surface of the gear is provided with (i) first and second protrusions that protrude toward the outer flat surface of the shaft so as to contact with the outer flat surface of the shaft, thereby providing an interference fit between the inner peripheral surface of the gear and the outer peripheral surface of the shaft, and (ii) a concave portion between the first and second protrusions that is apart from the outer flat surface of the shaft.