A pressure maintaining device for a resin injecting system, including a first chamber that can be connected to a pressurizing device and is able to be connected to a vacuum generating device; a second chamber that can be connected to a resin injection network of the injection system by a resin injection pipe and a resin outlet pipe, the first chamber and the second chamber being arranged so that the one is unable to leak into the other; a flexible body able to transmit pressurizing of the first chamber to the second chamber so as to apply pressure to the injection network of the injection system; a perforated rigid plate able to limit the deformation of the flexible body when the vacuum is created in the first chamber.