To suppress deterioration in the image quality caused by faulty fixing, without temporarily interrupting image forming processing, when collectively printing a series of a plurality of print jobs.

When the data of the plurality of print jobs are printed, the temperature variation estimated value of a fixing device, when performing each print job is calculated for each print job (S1), and performing order of all the print jobs is rearranged (S5), on the basis of present temperature of the fixing device, fixing target temperature of each print job and the temperature variation estimated value of the fixing device when performing each print job; and then the rearranged print jobs are performed in the order, so as to perform image forming processing (S6 and S7). When the temperature variation estimated value does not lie within tolerance, it is appropriate that the print job be divided (S2 and S3).