A catalytic reactor is provided comprising a plurality of first flow channels including a catalyst for a first reaction; a plurality of second flow channels arranged alternately with the first flow channels; adjacent first and second flow channels being separated by a divider plate (13a, 13b), and a distributed temperature sensor such as an optical fibre cable (19). The distributed temperature sensor may be located within the divider plate, or within one or 10 more of the flow channels.

An aspect of a chemical synthesis device according to the invention includes a substrate in which a channel for chemically synthesizing a plurality of fluids with each other is formed, and a wiring portion that is provided in the substrate, in which an electric resistance value of the wiring portion changes due to the wiring portion coming into contact with the fluids.

A flow passage structure is provided with a fluid flow passage that includes a plurality of straight flow passages, a first return bend that connects the downstream end of the straight flow passage through which a fluid flows from a second end surface toward a first end surface among the plurality of straight flow passages to the upstream end of the straight flow passage which is disposed at the downstream side of the straight flow passage and is adjacent to the straight flow passage, and a second return bend that connects the downstream end of the straight flow passage through which the fluid flows from the first end surface toward the second end surface among the plurality of straight flow passages to the upstream end of the straight flow passage which is disposed at the downstream side of the straight flow passage and is adjacent to the straight flow passage.