To provide a compact fixing device that reduces power consumption and a warm-up time, and an image forming apparatus.

A fixing unit is configured by including a fixing roller 61, a tension roller 63, an endless fixing belt 60 that is laid over the fixing roller 61 and the tension roller 63, a heater unit 64 that heats the fixing belt 60, and a pressure roller 62 with which the fixing roller 61 comes into pressure-contact via the fixing belt 60. The heater unit 64 is arranged to come into pressure-contact with the fixing belt 60; and the tension roller 63 has a heat insulating layer 63b arranged on an outer periphery that contacts the fixing belt 60.