A development apparatus has a casing, a regulation plate, a smoky dust
prevention sheet and a backup member which are fixed together onto the
casing with a screw. The backup member sandwiches a fixed end portion of
the smoky dust prevention sheet with the regulation plate. Therefore, the
backup member suppresses detachment of the smoky dust prevention sheet
from the regulation plate. Thus, the smoky dust prevention sheet is
prevented from being detached from the regulation plate when the smoky
dust prevention sheet is used in contact with a development roller in the
state of being bended.