A charged particle beam writing apparatus includes a buffer memory including a memory region capable of contemporarily storing writing data for data processing regions, wherein writing data including data files is temporarily stored for each of the data processing regions, a dividing unit to divide the memory region of the buffer memory into a first region being large and a second region being small, a specifying unit to specify the memory region such that a data file being large is preferentially stored in the first region and a data file being small is stored at least in the second region, concerning the data files for each of the data processing regions included in the writing data, and a data processing unit to read data files corresponding to each of the data processing regions from the buffer memory, and to perform data processing using the read data files.