A lithography process window analyzing method for setting a process window based on ranges of exposure amounts and focus positions, and giving evaluation of reliability of the set process window, includes setting, based on a plurality of process conditions including exposure amounts and focus positions in the performed exposure processing, analysis reliability M for process conditions including an arbitrary exposure amount and an arbitrary focus position; calculating reliability R of the process window based on the analysis reliability M concerning the process conditions included in the process window; and comparing a magnitude relation between the reliability R and a predetermined threshold and determining presence or absence of reliability of the process window according to a result of the comparison.