A production method is provided for obtaining a biologically ingestible material having an intended diameter with low energy as compared with conventional methods. The method includes mixing a fluid to be processed in a dispersed phase containing a pharmacologically active substance and a fluid to be processed in a continuous phase including at least a disperse solvent, while each of the fluids is retained in an independent state, in a thin film fluid formed between two processing surfaces arranged to be opposite to each other to be able to approach to and separate from each other, at least one of which rotates relative to the other, through independent pathways corresponding to the respective phases, whereby the components contained in the fluid to be processed in a dispersed phase are formed into microparticles having a desired diameter.
