A microreactor capable of reaction between a sample and a mixed reagent containing a mixture of multiple reagents, which microreactor avoids the interposition of air between driving solution and reagents and realizes high-precision controlling of the timing of mixing of reagents and other liquids, the mixing ratio of liquids, the pressure for liquid feeding, etc. Further, there is provided a method of liquid feeding making use of the same. Accordingly, a flow path branched at the position of an inlet from a flow path through which an opening communicating with an external pump communicates with the inlet is provided with an air evacuation flow path with its terminal open outward. Further, the flow path resistance of the air evacuation flow path for a liquid is made greater than the flow path resistance, for the liquid, of a flow channel from the reagent storage chamber to a reagent feed-out flow path.