A micro-reactor for analyzing a sample, comprises (1) a plate-shaped chip; (2) a plurality of regent storage sections each having a chamber to store respective agents; (3) a regent mixing section to mix plural regents fed from the plurality of regent storage sections so as to produce a mixed reagent; (4) a sample receiving section having an injection port through which a sample is injected from outside; and (5) a reacting section to mix and react the mixed regent fed from the reagent mixing section and the sample fed from the sample receiving section. The plurality of regent storage sections, the regent mixing section, the sample receiving section and the reacting section are incorporated in the chip and are connected through flow paths, and the regent mixing section includes a feed-out preventing mechanism to prevent an initially-mixed regent from being fed out to the reacting section.