To provide a simulating method with which scattering state can be simulated at a good accuracy to an additive used for a casting process.

Conditions for simulating flowing of molten metal, are inputted (S1) and a virtual grain having zero of the volume and zero of the mass, is disposed at a position for arranging the additive and the flowing of the molten metal is simulated (S3, S4) and also, the virtual grain is shifted along the flowing of the molten metal (S5). In this way, the scattering state of the additive can accurately be simulated.