A process unit comprising: a first casing having a photoconductor on which an electrostatic latent image can be formed and a developing cartridge, comprising: a developer carrier configured to carry a developer; a second casing having a pair of side plates which are configured to respectively support longitudinal end parts of the developer carrier; a first electrode configured to input a bias to the developer carrier; a receiving part integrally provided on one of the side plates and a joint member fixed to the receiving part, configured to join the first electrode to one of the side plates, and configured to urge the first electrode in a first direction perpendicular to the one of the side plates, thereby joining the second casing; wherein the first casing comprises: a first accommodating section configured to accommodate the developing cartridge so that the developer carrier is opposed to the photoconductor in a second direction, the first accommodating section having an engagement portion configured such that the first electrode of the developing cartridge enters the engagement portion in a third direction intersecting the second direction to be engaged with and fixed to the engagement portion when the developing cartridge is accommodated in the first accommodating section; and the second casing of the developing cartridge is configured to support the developer carrier, and is configured to move relative to the first electrode in the second direction when the developing cartridge is accommodated in the first accommodating section and wherein the receiving part and the first electrode are configured to relatively move to each other in the second direction in which the developer carrier and the photoconductor are opposed when the developing cartridge is accommodated in the first accommodation section. a first casing having a photoconductor on which an electrostatic latent image can be formed and a developing cartridge, comprising: a developer carrier configured to carry a developer; a second casing having a pair of side plates which are configured to respectively support longitudinal end parts of the developer carrier; a first electrode configured to input a bias to the developer carrier; a receiving part integrally provided on one of the side plates and a joint member fixed to the receiving part, configured to join the first electrode to one of the side plates, and configured to urge the first electrode in a first direction perpendicular to the one of the side plates, thereby joining the second casing; wherein a developer carrier configured to carry a developer; a second casing having a pair of side plates which are configured to respectively support longitudinal end parts of the developer carrier; a first electrode configured to input a bias to the developer carrier; a receiving part integrally provided on one of the side plates and a joint member fixed to the receiving part, configured to join the first electrode to one of the side plates, and configured to urge the first electrode in a first direction perpendicular to the one of the side plates, thereby joining the second casing; wherein the first casing comprises: a first accommodating section configured to accommodate the developing cartridge so that the developer carrier is opposed to the photoconductor in a second direction, the first accommodating section having an engagement portion configured such that the first electrode of the developing cartridge enters the engagement portion in a third direction intersecting the second direction to be engaged with and fixed to the engagement portion when the developing cartridge is accommodated in the first accommodating section; and the second casing of the developing cartridge is configured to support the developer carrier, and is configured to move relative to the first electrode in the second direction when the developing cartridge is accommodated in the first accommodating section and wherein the receiving part and the first electrode are configured to relatively move to each other in the second direction in which the developer carrier and the photoconductor are opposed when the developing cartridge is accommodated in the first accommodation section. a first accommodating section configured to accommodate the developing cartridge so that the developer carrier is opposed to the photoconductor in a second direction, the first accommodating section having an engagement portion configured such that the first electrode of the developing cartridge enters the engagement portion in a third direction intersecting the second direction to be engaged with and fixed to the engagement portion when the developing cartridge is accommodated in the first accommodating section; and the second casing of the developing cartridge is configured to support the developer carrier, and is configured to move relative to the first electrode in the second direction when the developing cartridge is accommodated in the first accommodating section and wherein the receiving part and the first electrode are configured to relatively move to each other in the second direction in which the developer carrier and the photoconductor are opposed when the developing cartridge is accommodated in the first accommodation section.