A fixing device includes a fixing belt, a heating roller and a fixing roller over which the fixing belt is looped, a pressure roller forming a fixing nip with the fixing belt, a pair of side plates, one of the side plates being disposed on each end of a shaft of the fixing roller and each end of a shaft of the heating roller, and heating roller holding members to hold corresponding insulating bushing, and corresponding heating roller bearings, the heating roller holding members being attached to opening parts of the side plates. The heating roller holding members are formed of two separate components such that the heating roller is capable of moving along the opening parts formed in the side plates toward the fixing roller.