A charged particle beam writing apparatus according to an embodiment, includes a dose coefficient calculation unit to calculate an n-th dose correction coefficient in iterative calculation of a charged particle beam to be shot in a small region concerned by the iterative calculation, for each small region of small regions made by virtually dividing into mesh-like regions, a change rate calculation unit to calculate, for each small region, a rate of change from an (n-1)th dose correction coefficient to the n-th dose correction coefficient calculated in the iterative calculation, as an n-th change rate, a correction calculation unit to correct, for each small region, the n-th dose correction coefficient by using the n-th change rate, and a dose calculation unit to calculate, for each small region, a dose of a charged particle beam to be shot in a small region concerned by using the n-th dose correction coefficient corrected.