In order to enable the computation of a process window including an arbitrary exposure condition, the present invention comprises: a contour data extraction means for extracting contour data from captured images of a plurality of circuit patterns formed by altering exposure conditions for identical design layouts; a shape variation measurement means for measuring, on the basis of the plurality of sets of extracted contour data, the amount of shape deformation at each edge or local region of the circuit patterns; a variation model computation means for computing, on the basis of the measured amount of shape deformation, a variation model for the contour data of a circuit pattern or a shape corresponding to a prescribed exposure condition; and a process window computation means using the variation model to estimate the amount of shape variation of a circuit pattern or a shape corresponding to an arbitrary exposure condition with respect to a circuit pattern or a shape corresponding to an exposure condition specified by a reference exposure condition and compute a process window on the basis of the estimated amount of shape variation.