1. A method of measuring beam positions of multi charged particle beams comprising: acquiring a number of beams of multi charged particle beams, needed for a measurement reproducibility of a current amount to be within a range of an allowable value; setting a plurality of measurement points depending on a desired dimensional accuracy value, in an irradiation region irradiated with a whole of the multi charged particle beams; setting, for each of the plurality of measurement points, a beam region, including a measurement point of the plurality of measurement points, irradiated by a plurality of beams whose number is the number of beams needed for the measurement reproducibility in the multi charged particle beams; and measuring, for the each of the plurality of measurement points, a position of a measurement point concerned in the plurality of measurement points by using the plurality of beams of a corresponding beam region.