Provided is a method for preventing a processed material from adhering to a processing surface constituting a flow path for a fluid to be processed, in a fluid processing method for mixing a fluid to be processed in a thin film fluid formed between at least two oppositely arranged processing surfaces capable of being brought together and moved apart, at least one rotating in a relative manner with respect to the other; and for obtaining a processed material. There are used at least two types of fluids to be processed among a raw material fluid including at least one type of raw material substance, and a fluid for processing the raw material substance; the fluids to be processed are mixed in a thin film fluids formed between at least two oppositely arranged processing surfaces (1, 2) capable of being brought together and moved apart, at least one rotating in a relative manner with respect to the other; and a processed material is obtained. The raw material fluid is introduced from the middle of the processing surfaces (1, 2), whereby the raw material substance processed in the space between the processing surfaces (1, 2) is prevented from adhering to the processing surfaces (1, 2).