A multi charged particle beam writing apparatus includes a maximum irradiation time acquisition processing circuitry to acquire, for each shot of multi-beams, a maximum irradiation time of irradiation time of each of the multi-beams, a unit region writing time calculation processing circuitry to calculate, using the maximum irradiation time for each shot, a unit region writing time by totalizing the maximum irradiation time of each shot of a plurality of times of shots of the multi-beams which irradiate a unit region concerned during stage moving, for each unit region of a plurality of unit regions obtained by dividing a writing region of a target object, a stage speed calculation processing circuitry to calculate speed of the stage for each unit region so that the stage speed becomes variable, by using the unit region writing time and a stage control processing circuitry to variably control the stage speed.