A heat exchange reactor comprising: reaction tubes for while allowing starting compound (A) to pass therethrough, effecting an exothermic reaction to thereby obtain product (B), and a reactor shell covering the surrounding area of the reaction tubes and having its interior divided into multiple regions along the direction of passage of the starting compound (A), each of which is filled with a heat medium, each of the regions adapted to carry out a heat exchange between the interior of reaction tube and the heat medium, characterized in that the heat exchange reactor is furnished with a heater capable of heating the heat medium charged in the upstreammost region among the regions resulting from the division independently from the heat medium charged in other regions.