An image forming apparatus includes an image forming unit that forms an image on a recording medium; a recording medium stacking unit including a stacking member having a stacking surface on which the recording medium having the image formed by the image forming unit is stacked, an outside member that is located at the outside of the stacking surface so as to extend in a substantially vertical direction to the stacking surface and detachably mounted in the recording medium stacking unit, and a support member having a support portion that supports the stacking member; an outside member recognizing unit that recognizes whether the outside member is mounted on the recording medium stacking unit, or not; and a controller that controls one of a maximum number of recording media to be stacked and a maximum height of stack of recording media in the recording medium stacking unit according to whether the outside member recognizing unit recognizes that the outside member is mounted, or not.