A microreactor containing a plurality of introduction channels 21 and 22 for introducing a plurality of liquids, a merging section 23 for merging the plurality of introduction channels 21 and 22, and a reaction channel 41 located on a downstream side of the merging section 23, characterized in that a flow control section 80 is located on a downstream side of the merging section 23 and an upstream side of the reaction channel 41, and the flow control section 80 contains in a channel 81 thereof a movable particle 82. According to the constitution, such a microreactor can be provided that the flow state in the reaction channel 41 is controlled to realize a flow state with good reproducibility.