An image forming apparatus includes a mounting portion where an image forming unit, detachably mountable to the image forming apparatus, for forming an image is mounted; an inserting opening for permitting insertion of the image forming unit into the mounting portion; a cover portion for opening and closing the inserting opening; a locking portion capable of being elastically displaced between a locking position where the image forming unit is locked at an image formable mounting position and a releasing position where locking is released; and a limiting mechanism for limiting movement of the locking portion by moving to a first position where the movement of the locking portion to the releasing position is prevented when the cover portion is closed and by moving to a second position where the movement of the locking portion to the releasing position is permitted when the cover portion is opened.