A beam dose computing method includes specifying a matrix of rows and columns of regions as divided from a surface area of a target object to include first, second and third regions of different sizes, the third regions being less in size than the first and second regions, determining first corrected doses of a charged particle beam for correcting fogging effects in the first regions, determining corrected size values for correcting pattern line width deviations occurring due to loading effects in the second regions, using said corrected size values in said second regions to create a map of base doses of the beam in respective ones of said second regions, using said corrected size values to prepare a map of proximity effect correction coefficients in respective ones of said second regions, using the maps to determine second corrected doses of said beam for correction of proximity effects in said third regions, and using the first and second corrected doses to determine an actual beam dose at each position on the surface of said object.