A fixing device and an image forming apparatus having the fixing device are provided. The fixing device includes at least two support members, a belt wound on the support members and supported to be movable in a circumferential direction of the support members, a heating member compressed to the belt, and a heat source heating the heating member. A recording medium electrostatically carrying a toner image passes through a fixing nip section formed between the belt and the heating member, thereby heating and fixing the toner image onto the recording medium. Among suspended portions of the belt suspended between the support members, a first suspended portion is in a tensile state, and the second suspended portion is in a non-tensile state. The heating member contacts the outside of the tensile suspended portion to form the fixing nip section.