The history of organic synthesis began in the late 19th century, and examples of batch reactions in flasks have been reported since then. Continuous production systems for mass production, such as pipelines, have been used for a long time. And it was in the late 20th century that the micro flow reactions used in general organic synthesis started to attract attention. Flow reactions feature (1) high-speed mixing, (2) high heat exchange rate, and (3) accurate control of residence time, thereby allowing reactions under conditions where batch reactions cannot realized. The applicability of these reactors is increasing; for example, they can be used for a gas-liquid reaction, which is expected to increase contact surface area, and in column flow reactors that use highly active solid phase catalysts.