An image forming apparatus includes an apparatus main body, an image forming unit, a tray unit and an attaching portion. The tray unit includes a pivot portion. The sheet is placed on the tray unit in an open state. The tray unit is capable of making a sliding movement in an axial direction of the pivot portion in a closed state. The tray unit is attached to the attaching portion in the closed state. The tray unit includes a pair of hooks that project from opposite end parts in the axial direction and each includes a projection. The attaching portion includes a pair of openings and a pair of engaging portions. The projections are inserted into the opening. Engaged positions of the projections with the engaging portions are variable according to the sliding movement in the closed state of the tray unit.