A flow member and a reaction vessel are provided. The reaction vessel is constituted by the flow member together with a first reaction unit and a second reaction unit. The first reaction unit is provided inside with a first catalyst layer and including a first supply port and a first outflow port. The second reaction unit is provided inside with a second catalyst layer, including a second supply port and a second outflow port. The second reaction unit is provided below the first reaction unit. The flow member includes: a flow path forming part forming a flow path that causes a reaction liquid to flow down from an inside of the first reaction unit toward an inside of the second reaction unit; and a liquid extractor, configured to extract the reaction liquid to an outside of the flow path.