A microchannel structure including a dispersed-phase introduction channel which communicates with a dispersed-phase introduction inlet; a continuous-phase introduction channel which communicates with a continuous-phase introduction inlet; a discharge channel which communicates with a discharge outlet; a fine-particle formation channel; and a plurality of branch channels for dispersed-phase introduction which are microchannels; wherein one end of the fine-particle formation channel in a fluid traveling direction communicates with the continuous-phase introduction channel whereas the other end thereof communicates with the discharge channel; and wherein a side part of the dispersed-phase introduction channel and side part of the fine-particle formation channel communicate via the plurality of branch channel for dispersed-phase introduction.