A method is provided for automatically generating a simulation program which numerically solves a partial differential equation which governs a physical quantity in a non-rectangular real space domain. The real partial differential equation is solved according to a boundary-fitted method by first transforming the original partial differential equation from a real space to a normal space. The upper limit of user work area memory available on the data processing apparatus and the number of mesh points extracted from the real space domain shape are considered in the transformation and to an extent control the transformation rule. Two program statements are thus generated, the first of which allocates data area for the particular variables in the work area memory. The second program statement defines the value of each variable in terms of one factor. The final step combines the partial differential equation and the first and second program statements into a simulation program which is used to solve the original partial differential equation.