A W/O emulsion is produced from an aqueous solution containing a substance to be entrapped in a vesicle in a dissolved or suspended state and an oil phase containing an emulsifier; subsequently, the W/O emulsion is cooled to a temperature at which the aqueous solution of the W/O emulsion becomes a frozen particle and the oil phase maintains a liquid state, and the oil phase is removed; thereafter, an oil phase containing a vesicle constituent lipid is added to the frozen particle, and the obtained mixture is then stirred, so as to substitute the emulsifier on the surface of the frozen particle with the vesicle constituent lipid; and thereafter, an external water phase is added to the frozen particle coated with a lipid membrane, so as to hydrate the lipid membrane by the external water phase. This process achieves a high entrapment yield of a desired substance while controlling desired physical properties such as particle diameter.