To solve the problem that an existing microextraction device can expect only an extraction effect of a theoretical equilibrium stage, even in case a groove (microchannel) part is made long, as a shortcoming, because two different fluids can be allowed to flow in one direction (ordinary current), but are difficult to be allowed to flow in mutually opposite directions (countercurrent).

This microextraction device keeps the groove (microchannel) part divided in two parts by a membrane, and the two different fluids can be made to flow in the countercurrent directions with the membrane set in between. Further, in order to promote the movement of a target substance between intragroove fluids, a globule can be placed in the groove and each intragroove fluid can be stirred and mixed by the right-to-left movement of the globule.