A pattern density distribution and a dose distribution calculated using the pattern density distribution are multiplied by each other to calculate an exposure distribution. A fogging electron amount distribution is calculated using the exposure distribution and a function descriptive of a fogging spread distribution. Charge amount distributions in irradiation and non-irradiation regions are calculated using the exposure distribution and the fogging electron amount distribution. A position displacement amount distribution is calculated using the charge amount distributions and a response function for converting a charge amount to a position displacement error.