An image forming apparatus capable of quickly heating a fixing belt with a simple configuration and stably maintaining the temperature of the fixing belt includes a fixing unit having a fixing belt, a fixing roller which supports a portion of the fixing belt and has a first heat source disposed therein, a heat transfer member which supports another portion of the fixing belt and transfers heat to the fixing belt, a pressing member which forms a fixing nip through which the fixing belt circulates, and a second heat source which is disposed outside the fixing roller and the heat transfer member and inside the fixing belt. The second heat source is disposed to heat at least two of the fixing belt, the fixing roller, and the heat transfer member.