A developing cartridge comprising: a developing roller rotatable about a developing roller-axis extending in a first direction; a casing configured to accommodate developing agent therein, the casing having an outer surface positioned at one end portion in the first direction of the casing ; a first shaft positioned at the outer surface of the casing and rotatable about a rotational axis (A) extending in the first direction, the first shaft having an outer periphery; a first arm extending radially outward from the outer periphery of the first shaft , the first arm being pivotally movable about the rotational axis (A) along with rotation of the first shaft ; and a cam extending radially outward from the outer periphery of the first shaft in a direction different from a direction in which the first arm extends, the cam being pivotally movable about the rotational axis (A) along with the rotation of the first shaft , the cam having: one end connected to the first shaft ; another end positioned farther from the rotational axis (A) than the one end is farther from the rotational axis (A); and a pressure contact surface inclined so as to approach the outer surface of the casing as extending from the one end toward the another end , wherein, when a pressing force is applied to the pressure contact surface , the first arm pivotally moves from a first position to a second position along with pivotal movement of the cam and along with the rotation of the first shaft . a developing roller rotatable about a developing roller-axis extending in a first direction; a casing configured to accommodate developing agent therein, the casing having an outer surface positioned at one end portion in the first direction of the casing ; a first shaft positioned at the outer surface of the casing and rotatable about a rotational axis (A) extending in the first direction, the first shaft having an outer periphery; a first arm extending radially outward from the outer periphery of the first shaft , the first arm being pivotally movable about the rotational axis (A) along with rotation of the first shaft ; and a cam extending radially outward from the outer periphery of the first shaft in a direction different from a direction in which the first arm extends, the cam being pivotally movable about the rotational axis (A) along with the rotation of the first shaft , the cam having: one end connected to the first shaft ; another end positioned farther from the rotational axis (A) than the one end is farther from the rotational axis (A); and a pressure contact surface inclined so as to approach the outer surface of the casing as extending from the one end toward the another end , one end connected to the first shaft ; another end positioned farther from the rotational axis (A) than the one end is farther from the rotational axis (A); and a pressure contact surface inclined so as to approach the outer surface of the casing as extending from the one end toward the another end , wherein, when a pressing force is applied to the pressure contact surface , the first arm pivotally moves from a first position to a second position along with pivotal movement of the cam and along with the rotation of the first shaft . <EOS>