A developer cartridge is configured to be detachably mounted in an apparatus main body and to accommodate developer. The developer cartridge includes a drive member and a display portion. The drive member is configured to be driven to move by a driving force when the developer cartridge is mounted in the apparatus main body. The display portion is configured to move together with the drive member. The display portion displays identification information relating to the developer cartridge in an optically readable manner. A detecting portion optically detects the identification information when the display portion is in a first position, and optically detects presence or absence of the developer in the developer cartridge when the display portion is in a second position different from the first position. An information determining portion determines information on the developer cartridge based on the identification information detected by the detecting portion.