Reactor and production thereof, reformer, and power supply system

A reactor includes paired channels for allowing chemical reactions of fluids. The paired channels are formed on a substrate such that they extend close to and along each other. They are provided with a heat exchanger performing heat exchange between them. Independent claims are also included for: (1) producing a reactor having paired channels by forming on a substrate paired channels arranged close to and along each other; forming on another substrate a heat exchanger for heat exchange between the paired channels; and bonding the two substrates together; (2) a reformer (2) comprising paired channels to reform a fluid flowing through the channels; and (3) a power supply system (1) comprising a reformer and a power generator (3).