To highly accurately estimate a shape of a pattern actually transferred only through calculations, by obtaining form calculations a light intensity distribution on a photoresist exposed in a defocused state.

A light-shielding film pattern formed on a photomask 2 is reduced, projected and exposed via a projecting lens 3 on a photoresist 5 applied on a substrate 4 to be processed. Supposing that the pattern is defocused by a defocus amount df to a best focus position 6, a light intensity distribution on the photoresist 5 is calculated. A shape of a transfer pattern to a design pattern is estimated from the calculated intensity distribution. In this case, as compared with when the pattern is exposed at the best focus position 6, the obtained shape of the transfer pattern is closer to a pattern actually transferred.