The partial differential equations inputted with respect to an unknown quantity A are processed according to the finite element method in which simultaneous first-order equations equivalent to the partial differential equations are obtained, and then a matrix equation equivalent to the simultaneous first-order equations, namely, (k.sub.ij) (a.sub.i)=(d.sub.i) is processed to derive a coefficient {a.sub.j } so as to generate a program which calculates the unknown quantity A. For each group of a plurality of elements, the program calculates a contribution determined by the positions of the nodes associated with the elements with respect to a portion of matrix element group such as k.sub.lm and k.sub.ll and a portion of constant group such as d.sub.l and d.sub.m determined by the numbers assigned to a plurality of nodes contained in the group of a plurality of elements and then generates the final values of the matrix element group {k.sub.ij } and the constant {d.sub.i } from the contribution calculated for each group of a plurality of elements.