The present invention provides a fixing device capable of reliably preventing non-conveyance paper spans of a fixing belt from overheating and an image forming apparatus. The fixing device includes a shield member (27) rotating around a halogen heater pair (23) (heating source) and shielding the heat from the halogen heater pair (23) to a fixing belt (21) (fixing member), and a controller for controlling a rotation angle of the shield member (27), the shield member (27) comprising a shield portion (48) disposed in an area covering one part of an axial direction of the halogen heater pair (23) and a recess (50) adjacent to one side of the axial direction of the shield portion (48), the shield portion (48) extending along an internal peripheral surface of the fixing belt (21) and having a shape with ends in a peripheral direction, and the controller determining the rotation angle of the shield member (27) based on the size of a paper and the temperature of the fixing belt (21) or a pressing roller (22).