A fusing unit is formed along a printing path in an image forming apparatus and fuses an image transferred to a printing medium. The fusing unit includes: a heat source; a nip plate which is heated by the heat source, and comprises a nip part to heat and press the printing medium; and a reflection member to reflect heat generated by the heat source toward the nip part. A belt member is rotatably provided about the heat source, the nip plate and the reflection member, and guides the movement of the printing medium. A driving roller faces the nip part and rotatably drives the belt member. The nip plate and the driving roller form a fusing nip, which quickly heats and provides for quick fusing of a toner image to a printing medium.