An image forming apparatus includes an image forming portion, an endless belt and a plurality of stretching rollers. The stretching rollers includes a tiltable steering roller, a sliding member, a first stretching roller having a smallest diameter, and a second stretching roller having a largest diameter of the diameters. With respect to rotational axis directions of the stretching rollers, lengths of contact portions of the stretching rollers with the belt are shorter than a width of the belt, the length of the contact portion of the first stretching roller with the belt is a first length, the length of the contact portion of the second stretching roller with the belt is a second length shorter than the first length, and end positions of the contact portions of the first and second stretching rollers with respect to the rotational axis direction are different from each other.