A compact desktop continuous stirred tank reactor easily used on a magnetic stirrer is provided. A desktop continuous stirred tank reactor used on a magnetic stirrer includes a plurality of containers, each of the plurality of containers having a bottom and a shape capable of containing a stir bar, the plurality of containers being configured as a single unit member. The plurality of containers is arranged on the circumference of a circle of rotation of a pair of magnets of the magnetic stirrer or inside the circumference, and adjacent containers communicate through communication holes.