A mixer and a reactor including the same are provided. According to one aspect of the present invention, the mixer includes a first piping part into which a first fluid flows, an elbow piping part having an inlet connected to the first piping part and an outlet provided at a location rotated by a predetermined angle from the inlet in a flow direction of the first fluid to have a curved flow path, and a second piping part connected to the elbow piping part to have a central axis perpendicular to a central axis of the first piping part so that a second fluid flows in a tangential direction of the elbow piping part when the second fluid flows into the elbow piping part.