1. A pattern evaluation method comprising: acquiring an aberration parameter of an image quality evaluation apparatus for determining a pattern image intensity in transferring a pattern formed on a photomask onto a wafer; setting an acceptance criterion value used in determining whether an abnormal pattern of the photomask including the effect of aberration of the image quality evaluation apparatus is acceptable, through a lithographic simulation using the acquired aberration parameter; acquiring an image intensity of the abnormal pattern of the photomask and an image intensity of a normal pattern corresponding to the abnormal pattern with the image quality evaluation apparatus; and determining whether the difference between the two acquired image intensities is within the set acceptance criterion value.