To provide an image forming apparatus that facilitates removal work of a belt unit.

The belt unit 30 includes: a rocking shaft part 30A provided to the tip in the attaching direction D1; and an engagement protrusion 35A projecting in the width direction of an endless belt 33. The engagement protrusion 35A is provided between a cyclic axis C1 on the rear end in the attaching direction D1 of the endless belt 33, and the rocking shaft part 30A. The device body includes a rocking support part 3A which is provided to the tip in the attaching direction D1 and rockably supports the belt unit 30 around a horizontal rocking axis S1 perpendicular to the attaching direction by engagement with the rocking shaft part 30A in attaching the belt unit 20. A locking mechanism contacts the engagement protrusion 35A while applying an biasing force F1 and fixes the belt unit 30 to an operation position when the belt unit 30 is attached and when the rocking shaft part 30A engages with the rocking support part 3A and the belt unit 30 rocks around the rocking axis S1.