In order to simultaneously prevent both curl generation and fixation performance deterioration upon both-surface image formation of a recording medium P, a fixation temperature control means which subjects a transporting-direction trailing end region of a first surface (front surface) of the recording medium P to fixation at a low heating treatment temperature, thereby suppressing the curl generation amount in the region subjected to the low-temperature heating treatment, at the same time, subjects the region except for the region that has undergone the low-temperature heating treatment to fixation at a normal heating treatment temperature, thereby preventing deterioration in the fixation performance, and subjects the region which has undergone the low-temperature heating treatment to heating treatment of a high temperature upon fixation of a second surface (back surface), thereby preventing defective fixation in the low-temperature heating treatment region is provided.