A method for writing a pattern on an object by a charged particle beam comprises the steps of: dividing a pattern to be written on the object into a plurality of pattern blocks that cause a proximity effect with each other; determining a pattern density for each of said pattern blocks; selecting a specific pattern block as a reference pattern block; setting a dose level of exposure of the charged particle beam to a reference dose level such that the reference pattern block is exposed with a predetermined total dose level which includes the contribution of the exposure by the charged particle beam and the contribution of the exposure by the backscattered charged particles; exposing the plurality of pattern blocks including the reference pattern block by the charged particle beam with the reference dose level; and exposing those pattern blocks that have the pattern density smaller than the pattern density of the reference pattern block by a defocused charged particle beam with a total dose level set such that the total dose level for those pattern blocks is substantially identical with the total dose level of the reference pattern block.