To obtain a heat exchanger apparatus capable of securing a sufficient heat exchanging amount per unit time.

A cooling fluid supply pipe 23 and a steam supply pipe 3 are connected to a jacket part 11 of a reaction vessel 1. A second heat exchanger 31 is mounted to the inside of the reaction vessel 1. A sub heat exchanger 27 is mounted to the outside of the jacket part 11. Upper and lower parts of the sub heat exchanger 27 are connected inside the reaction vessel 1 via a circulation pump 28. A steam trap 25 is connected to a lower part of a gas-liquid separator 4. A fluid supply pipe 6 is connected between a steam pressure adjustment valve 7 and the gas-liquid separator 4. A liquid ejector 20 intervenes in the fluid supply pipe 6. A suction chamber 22 of the liquid ejector 20 is connected to an outlet side of the steam trap 25. At the inside of the jacket part 11, the reaction vessel 1 is heat exchanged and also heat-exchanged by the second heat exchanger 31. At the outside of the jacket part 11, the sub heat exchanger 27 is heat-exchanged.