A developing unit containing developer including carrier and toner and
developing a latent image formed on an image carrier is disclosed. The
developing unit includes multiple conveyor members configured to convey
the contained developer in respective longitudinal directions so as to
form a circulation channel; a supply part configured to supplement the
carrier in the developing unit; a discharge part configured to discharge
a first part of the contained developer outside the developing unit; and
a bypass channel configured to cause a second part of the developer to
return to the upstream side of the circulation channel without passing a
position where the discharge part is provided.