A developing cartridge comprising: a casing configured to accommodate therein developing agent; a developing roller rotatable about a developing-roller axis extending in a first direction and contactable with a photosensitive drum , the developing roller having a peripheral surface a portion of which is exposed to an outside of the casing in a second direction, another portion of the peripheral surface opposite the exposed portion in the second direction being positioned inside the casing ; and a first cam positioned at an outer surface of one end portion of the casing in the second direction, the first cam being movable in a third direction relative to the casing and the developing roller between a first position and a second position, the second position being closer to the developing roller than the first position is to the developing roller in the third direction, the first cam having: a first inclined surface configured to receive a pressing force directing from one end portion of the casing in the first direction toward another end portion of the casing in the first direction; and a second inclined surface , a distance in the second direction between the second inclined surface and the casing varying as the second inclined surface extends away from the developing roller in the third direction, wherein the first cam is movable between the first position and the second position in response to application of the pressing force (F) to the first inclined surface . a casing configured to accommodate therein developing agent; a developing roller rotatable about a developing-roller axis extending in a first direction and contactable with a photosensitive drum , the developing roller having a peripheral surface a portion of which is exposed to an outside of the casing in a second direction, another portion of the peripheral surface opposite the exposed portion in the second direction being positioned inside the casing ; and a first cam positioned at an outer surface of one end portion of the casing in the second direction, the first cam being movable in a third direction relative to the casing and the developing roller between a first position and a second position, the second position being closer to the developing roller than the first position is to the developing roller in the third direction, the first cam having: a first inclined surface configured to receive a pressing force directing from one end portion of the casing in the first direction toward another end portion of the casing in the first direction; and a second inclined surface , a distance in the second direction between the second inclined surface and the casing varying as the second inclined surface extends away from the developing roller in the third direction, a first inclined surface configured to receive a pressing force directing from one end portion of the casing in the first direction toward another end portion of the casing in the first direction; and a second inclined surface , a distance in the second direction between the second inclined surface and the casing varying as the second inclined surface extends away from the developing roller in the third direction, wherein the first cam is movable between the first position and the second position in response to application of the pressing force (F) to the first inclined surface . <EOS>