A developing cartridge attachable to a drum unit , the developing cartridge comprising: a casing in which developing agent is accommodatable; a developing roller movable together with the casing and comprising a developing roller shaft extending along a first axis (A1) extending in a first direction, the developing roller being rotatable about the first axis (A1); a first electrode positioned at one end portion in the first direction of the developing roller shaft , and electrically connected to the developing roller shaft ; and a boss positioned at one end portion in the first direction of an outer surface of the casing , the boss extending in the first direction, wherein a part of the first electrode is configured to contact with a second electrode of the drum unit as a result of pivotal movement of the developing cartridge about the boss relative to the drum unit in a case where the developing cartridge is attached to the drum unit , and characterized in that the first electrode covers at least a part of an outer peripheral surface of the one end portion of the developing roller shaft , the first electrode has one of a recess and a through-hole allowing the one end portion of the developing roller shaft to be inserted therein, the developing roller is rotatable in a state of the insertion of the one end portion of the developing roller shaft in the one of the recess and the through-hole , the first electrode comprises a collar having the one of the recess and the through-hole , the collar including a small diameter portion and a large diameter portion having an outer diameter greater than that of the small diameter portion , and an outer peripheral surface of the small diameter portion and an end face in the first direction of the large diameter portion are in contact with the second electrode in a state where the developing cartridge is attached to the drum unit . a casing in which developing agent is accommodatable; a developing roller movable together with the casing and comprising a developing roller shaft extending along a first axis (A1) extending in a first direction, the developing roller being rotatable about the first axis (A1); a first electrode positioned at one end portion in the first direction of the developing roller shaft , and electrically connected to the developing roller shaft ; and a boss positioned at one end portion in the first direction of an outer surface of the casing , the boss extending in the first direction, wherein a part of the first electrode is configured to contact with a second electrode of the drum unit as a result of pivotal movement of the developing cartridge about the boss relative to the drum unit in a case where the developing cartridge is attached to the drum unit , and characterized in that the first electrode covers at least a part of an outer peripheral surface of the one end portion of the developing roller shaft , the first electrode has one of a recess and a through-hole allowing the one end portion of the developing roller shaft to be inserted therein, the developing roller is rotatable in a state of the insertion of the one end portion of the developing roller shaft in the one of the recess and the through-hole , the first electrode comprises a collar having the one of the recess and the through-hole , the collar including a small diameter portion and a large diameter portion having an outer diameter greater than that of the small diameter portion , and an outer peripheral surface of the small diameter portion and an end face in the first direction of the large diameter portion are in contact with the second electrode in a state where the developing cartridge is attached to the drum unit . <EOS>