A fixing device for fixing a toner image onto a recording medium, and an image forming apparatus having the same are provided. The fixing device includes a fixing roller heated by a heating source, and a pressing unit disposed opposite the fixing roller to bias a recording medium towards the fixing roller so that the recording medium contacts the fixing roller. The pressing unit has a movable support member, a pressing member mounted at the support member to face the fixing roller, a pressing belt rotatably disposed around the support member and the pressing member and biased by the pressing member to form a nip with the fixing roller, a driving roller for rotating the pressing belt, and a resilience applying member for biasing at least one of the support member and the driving roller toward the fixing roller. Accordingly, the pressing unit basically expands the width of the fixing nip to improve the image fixing capability.