A developing cartridge which is detachably mounted in an apparatus main body of an image forming apparatus, the developing cartridge comprising: a housing including a first side wall and a second side wall which are provided to oppose each other, the housing configured to accommodate developer therein; a receiving member provided on an outer side of the first side wall to be rotatable about a first axis which extends in an opposing direction of the first side wall and the second side wall, the receiving member configured to couple with a driving force output member provided in the apparatus main body to receive a driving force from the driving force output member; a developing roller provided between the first side wall and the second side wall to be rotatable about a second axis which extends in parallel to the first axis with a space therebetween, the developing roller configured to rotate by the driving force received by the receiving member; and a detectable rotary member provided on the outer side of the first side wall to be rotatable about a third axis which extends in parallel to the first axis with a space therebetween, and including a detectable portion, which is a detection target to be detected by a detection member provided in the apparatus main body, and a contact portion, the detectable rotary member configured to rotate from a retreat position to an initial position by the contact portion contacting an interference member fixed in the apparatus main body in a process of mounting the developing cartridge into the apparatus main body, the initial position being a position where the detectable rotary member is rotated by the driving force received by the receiving member, wherein each of the detectable portion and the contact portion extends in a radius direction of a rotation of the detectable rotary member, characterized in that the contact portion is provided away from the detectable portion in a rotational direction about the third axis,and the contact portion includes an abutment portion projecting outside a rotating locus drawn by the detectable portion when the detectable rotary member rotates, the abutment portion configured to contact the interference member. a housing including a first side wall and a second side wall which are provided to oppose each other, the housing configured to accommodate developer therein; a receiving member provided on an outer side of the first side wall to be rotatable about a first axis which extends in an opposing direction of the first side wall and the second side wall, the receiving member configured to couple with a driving force output member provided in the apparatus main body to receive a driving force from the driving force output member; a developing roller provided between the first side wall and the second side wall to be rotatable about a second axis which extends in parallel to the first axis with a space therebetween, the developing roller configured to rotate by the driving force received by the receiving member; and a detectable rotary member provided on the outer side of the first side wall to be rotatable about a third axis which extends in parallel to the first axis with a space therebetween, and including a detectable portion, which is a detection target to be detected by a detection member provided in the apparatus main body, and a contact portion, the detectable rotary member configured to rotate from a retreat position to an initial position by the contact portion contacting an interference member fixed in the apparatus main body in a process of mounting the developing cartridge into the apparatus main body, the initial position being a position where the detectable rotary member is rotated by the driving force received by the receiving member, wherein each of the detectable portion and the contact portion extends in a radius direction of a rotation of the detectable rotary member, characterized in that the contact portion is provided away from the detectable portion in a rotational direction about the third axis,and the contact portion includes an abutment portion projecting outside a rotating locus drawn by the detectable portion when the detectable rotary member rotates, the abutment portion configured to contact the interference member.