The mark position is measured with a multi-beam with high accuracy. A multi charged particle beam writing method includes forming a multi-beam in which charged particle beams are arranged with a predetermined pitch, irradiating a mark with beams in an on-beam region while shifting irradiation positions of the charged particle beams by sequentially changing the on-beam region in which beams in a partial region of the multi-beam are set to ON, the mark being provided at a predetermined position and having a width greater than the predetermined pitch, detecting a reflected charged particle signal from the mark, and calculating a position of the mark, and adjusting the irradiation positions of the multi-beam based on the calculated position of the mark, and writing a pattern.