A method of handling a continuum model in an inhomogeneous field using field variables called phase fields. By introducing a continuous field that describes the state of the phase in addition to the density and temperature fields as field variables, it can be applied to the simulation of many physical phenomena (solidification phenomena, phase transformation, etc.) accompanied by phase transition. The continuous field is described based on the Ginzburg-Landau equation, and the parameters in the model are determined by the phase free energies. Since all physical quantities are written in a continuous field, calculation codes are easy to write, and public or commercially available programs can be used.