A relative positional error is caused between an alignment mark and a device area on a mask due to an error inherent to the mask drawing apparatus, which causes an alignment error in the device area even when alignment upon exposure has no problem. Then, according to this invention, a relative positional error between the alignment mark and the device area on the mask is measured in an off line manner, the result of measurement is set upon exposure as a correction value to an exposure device thereby correcting the mask drawing error to reduce alignment errors in the device area.