A photosensitive unit is described. The photosensitive unit may include a developer cartridge including a developing agent carrier and a casing, a photosensitive member, and a side wall. The casing is provided with a pivoting member including a pressuring portion applied with an external pressing force and a fitting projection fitted to the side wall. The pivoting member is configured to be pivoted along a pressing direction for pressing the developing agent carrier toward the photosensitive member when a pressing force is applied to the pressuring portion, or along a pressure releasing direction opposite to the pressing direction. The side wall is formed with a fit portion to which the fitting projection is loosely fitted so that a movement of the fitting projection along a pivoting direction of the pivoting member is allowed.