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.

Provided is an image forming apparatus that together with being able to suppress rotation unevenness is capable of preventing unexpected downtime due to a broken belt. A guide member guides the swing of a swing gear on an arc that connects a first position where the swing gear is engaged with an idle gear, and a second position where the swing gear is not engaged with the idle gear. A transmission cutoff mechanism cuts off transmission of a drive force transmitted to a driven pulley via a belt to a driven shaft when a motor rotates in the reverse direction. A control unit, in a case where rotation unevenness meets a condition, causes the swing gear to swing to the first position by reverse rotation of the motor, which causes the drive force to be transmitted to the driven shaft.

Provided is an image forming apparatus that together with being able to suppress rotation unevenness is capable of preventing unexpected downtime due to a broken belt. A guide member guides the swing of a swing gear on an arc that connects a first position where the swing gear is engaged with an idle gear, and a second position where the swing gear is not engaged with the idle gear. A transmission cutoff mechanism cuts off transmission of a drive force transmitted to a driven pulley via a belt to a driven shaft when a motor rotates in the reverse direction. A control unit, in a case where rotation unevenness meets a condition, causes the swing gear to swing to the first position by reverse rotation of the motor, which causes the drive force to be transmitted to the driven shaft.

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.