there is provided a reaction apparatus which is capable of keeping the pressure inside the reactor and is applicable to various fields . this reaction apparatus comprises : a raw material tank for storing a raw material ; a high - pressure pump communicated with the raw material tank and designed to deliver the raw material therefrom ; a reactor which is disposed on the downstream side of the high - pressure pump and designed to be supplied with the raw material in a compressed state ; a heating bath for heating the reactor to promote a reaction ; and a product tank for receiving and recovering a product ; wherein the reaction apparatus is further equipped with an inlet port which is interposed between the heating bath and the product tank , and with an injection pump for injecting an injecting liquid through the inlet port , whereby a pressure of product flowing into the product tank is enabled to be reduced by making use of the flow rate of the injecting liquid .