Patent ID: 8280269

Claim:
A process cartridge detachably installable to a main frame of an image forming device, the main frame having a developing-agent amount detection unit including a light emitting element and a light receiving element, comprising: an image bearing member cartridge including: a first casing having a pair of first and second side plates defining an accommodation portion; a latent image bearing member having a surface on which an electrostatic latent image is formed, the latent image bearing member being supported to the first casing; and a pressure member; and a developing cartridge detachably installed in the accommodation portion and including: a second casing having a pair of third and fourth side plates in confrontation with the first and second side plates, respectively, the pair of third and fourth side plates defining a chamber that stores a developing agent; a developing agent bearing member rotatably supported to the second casing, the developing agent bearing member supplying the developing agent onto the latent image bearing member; and a pair of first and second light guides fixed to the third and fourth side plates, respectively, the pair of first and second light guides being configured to introduce a light emitted from the light emitting element into the chamber and to direct the light from the chamber toward the light receiving element, each of the first and second light guides having a fixed end portion having a first end surface and fixed to either of the third and fourth side plates, a free end portion having a second end surface and remote from the chamber, and a side surface extending in an axial direction of the developing agent bearing member, wherein: the pressure member presses the side surfaces, thereby urging the developing agent bearing member toward the latent image bearing member.