An image fixing unit includes a heating roller, a pressing roller forming
a first fixing nip by contact with an outer surface of the heating
roller, and a fixing nip expansion unit forming a second fixing nip by
contact with the heating roller. The fixing nip expansion unit includes
an auxiliary pressing member mounted at one side of the pressing roller
and forming the second fixing nip by contact with the outer surface of
the heating roller, an endless belt moving along a caterpillar track
surrounding outer circumferences of the heating roller and the auxiliary
pressing member, and a resilient unit biasing the heating roller and the
auxiliary pressing member resiliently toward the heating roller.