To provide an image forming apparatus having tandem fixing units, in which a time loss is substantially prevented even in the case of consecutive passage of sheets of paper and different sheet materials are prevented from being fixed at the same time in first and second fixing units.

N-number of sheet materials P are conveyed in blocks P1 to P3, blocks P4 to P6, and so on. A distance L' between the blocks P1 to P3 and blocks P4 to P6 is made longer than a distance L between the tandem fixing units 3A and 3B.