The effect of an antitumor aqueous solution that is generated through plasma irradiation varies in accordance with plasma irradiation conditions, and appropriate plasma irradiation conditions depend on the type of tumor. Thus, a problem to be addressed is to provide an antitumor aqueous solution manufacturing device capable of manufacturing an antitumor aqueous solution having an appropriate antitumor effect. An antitumor aqueous solution manufacturing device (10) according to the invention for addressing the problem is a device configured to manufacture an antitumor aqueous solution having an antitumor effect, the device including a stage (26) configured to hold a raw material solution in which a raw material of the antitumor aqueous solution is dissolved； a plasma generating device (20) configured to generate plasma to be radiated on the raw material solution held by the stage (26)； a hydrogen peroxide detection sensor (147) configured to measure a hydrogen peroxide concentration in the raw material solution； and a control device (38) configured to control the plasma generating device (20), the control device (38) controlling the plasma generating device (20) such that the hydrogen peroxide concentration measured by the hydrogen peroxide detection sensor (147) falls within a predetermined range.
