Disclosed herein is a micro-channel reactor formed by placing a planar upper plate and a planar lower plate, each having a channel formed therein, such that the upper plate and the lower plate face each other, wherein the channel includes one or more introduction channels, into which different fluids are introduced respectively, a mixing channel, along which the fluids introduced into the introduction channels flow in a state in which the fluids join each other, and a discharge channel, from which the fluids joining in the mixing channel are discharged, the mixing channel includes a stem channel extending from the introduction channels to the discharge channel and one or more branch channels that diverge from the stem channel and are then interrupted, and, when the fluids are mixed through repetitive diverging and joining, the fluids diverge in upward and downward directions and then join each other in leftward and rightward directions.