Provided is an apparatus for producing a joined-resin product in which two or more resin members are joined. The apparatus includes: a surface treatment mechanism comprising an electrode unit generating ionized gas, and a member holding mechanism arranged at a position separated from the electrode unit by a space and holding the resin member, the surface treatment mechanism activating a surface to be joined of the resin member held by the member holding mechanism, by the ionized gas generated by the electrode unit; and a joining mechanism bonding the two or more resin members together where at least one of surfaces to be joined facing each other is activated by the surface treatment mechanism, at the respective surfaces to be joined.