In accordance with one aspect of this invention, a multi charged particle beam writing apparatus includes an aperture member, in which a plurality of openings are formed, configured to form multi-beams by making portions of the charged particle beam pass through the plurality of openings; a plurality of blankers configured to perform blanking-deflect regarding beams corresponding to the multi-beams; a writing processing control unit configured to control writing processing with a plurality of beams having passed through different openings among the plurality of openings being irradiated on the target object at a predetermined control grid interval; and a dose controlling unit configured to variably control a dose of a beam associated with deviation according to a deviation amount when an interval between the plurality of beams irradiated is deviated from the control grid interval.