A multi charged particle beam writing apparatus according to an embodiment, includes a setting unit to set a second region such that more openings in remaining openings except for an opening through which the defective beam passes are included in the second region, a selection unit to select a mode from a first mode in which a pattern is written on a target object by using multiple beams having passed openings in the second region and a second mode in which multiple writing is performed while shifting a position by using at least one of remaining multiple beams in the state where the defective beam is controlled to be beam off and additional writing is performed for a position which was supposed to be written by the defective beam, and a writing processing control unit to control to write in the mode selected.