In an image forming apparatus having single-color mode and full-color mode, to maintain an excellent fusing property of the single-color image and the full-image even on the condition that the temperature of the fixing member is easy to fall, when the temperature of the fusing roller lowers during the image forming job, the control for decreasing the subsequent image productivity or the control for discontinuing the job is performed within general performance power supply with ease. The reference temperature for determining such lowering of the image productivity or discontinuation of the job is set to be lower in the single-color mode than the full-color mode. As a result, both of the fusing property and the high image productivity can be realized.