The present invention addresses the problem of providing a new method for increasing the production of fine particles. Using at least two types of fluids to be processed, a raw material fluid containing at least one type of fine particle raw material and a fluid for treating the fine particle raw material, fine particles are obtained by mixing the fluids to be processed in a thin film fluid formed between at least two processing surfaces which are disposed to be faced with each other so as to be able to approach to and separate from each other, at least one of which rotates relative to the other. At this time, the production of the fine particles is increased by introducing the raw material fluid from the centers of the processing surfaces.