A tension roller which is brought into contact with an inner circumferential surface of an endless belt and is rotated and which can be moved to a first position where the belt is in a relaxed state and a second position where the belt is in a tensioned state, a butting member which butts against the belt, a force application unit which applies, to the butting member, a force acting in a direction opposite to a rotation direction of the belt and a movement mechanism which moves the tension roller to the first position and the second position are provided. When the belt is rotated, the butting member is moved in the rotation direction of the belt by a friction force with the belt, and the movement mechanism moves the tension roller from the first position to the second position by the movement of the butting member in the rotation direction of the belt. When the rotation of the belt is stopped, the butting member is moved in the direction opposite to the rotation direction of the belt by the force applied by the force application unit, and the movement mechanism moves the tension roller from the second position to the first position by the movement of the butting member in the direction opposite to the rotation direction of the belt.