To provide an arrangement method for reactors capable of installing a plurality of reactors in a relatively small space while suppressing a thermal loss in the reactors.

Microreactors 3A-3F are formed in a similar shape and such a temperature gradient that the temperature is lowered according as it leaves from a base angle 11 is generated in the microreactors 3A-3F. The base 16 of microreactor 3A is brought into contact with a side 15 of microreactor 3B, the base 16 of microreactor 3B is brought into contact with a side 15 of microreactor 3C, the base 16 of microreactor 3C is brought into contact with a side 15 of microreactor 3D, the base 16 of microreactor 3D is brought into contact with the side 15 of microreactor 3E, the base 16 of microreactor 3E is brought into contact with the side 15 of microreactor 3F and the base angles 11 of microreactors 3A-3F are trued up.