A developer cartridge includes a casing, a development roller, a support
member, and at least one transmission gear. The development roller is
rotatably disposed in the casing. The support member is provided as a
separate member from the casing and is mounted on the casing. The at
least one transmission gear is rotatably supported by the support member.
The at least one transmission gear transmits a driving force to the
development roller. The support member is configured to be dismounted
from the casing together with the at least one transmission gear.