Reactor

A reactor utilizing heat exchange between a first fluid as a reaction fluid and a second fluid, the reactor comprising:

• a reaction unit including a first flow channel through which the first fluid flows and a second flow channel through which the second fluid flows;
• a first pipe communicating with the first flow channel so as to allow a third fluid containing a product produced in the reaction unit to flow through;
• a second pipe through which the second fluid is supplied to the second flow channel;
• a composition analysis unit connected to the first pipe so as to analyze a composition of the product;
• a regulating unit connected to the second pipe so as to regulate a flow rate and/or a temperature of the second fluid;
• a control unit causing the regulating unit to regulate the flow rate and/or the temperature of the second fluid in accordance with the composition of the product analyzed by the composition analysis unit so that a temperature of the third fluid is controlled to lead the composition of the product to keep a predetermined reaction rate or yield;
• and
• a first temperature measurement unit connected to the first pipe so as to measure the temperature of the third fluid,
• wherein the control unit acquires information on the temperature of the third fluid from the first temperature measurement unit.