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 (2) for storing a raw material; a high-pressure pump (3) communicated with the raw material tank (2) and designed to deliver the raw material therefrom; a reactor (1) which is disposed on the downstream side of the high-pressure pump (3) and designed to be supplied with the raw material in a compressed state; a heating bath (11) for heating the reactor (1) to promote a reaction; and a product tank (7) for receiving and recovering a product; wherein the reaction apparatus is further equipped with an inlet port which is interposed between the heating bath (11) and the product tank (7), and with an injection pump (6) for injecting an injecting liquid through the inlet port, whereby a pressure of product flowing into the product tank (7) is enabled to be reduced by making use of the flow rate of the injecting liquid.