at this time it is desirable that the mixture ratio of oxygen to nitrogen is from 0 01 1 to 0 5 1 however the ratio is not limited and it is possible to use mixed gas of nitrogen and oxygen at a certain ratio the polymerizing processing by the mixture of oxygen and nitrogen can be used to improve hydrophile as well as to strengthening every characteristic of the polymerized substrate such as a hydrophobe processed and corrosion prevented substrate the plasma polymerizing method is composed of the steps of polymerizing a surface of a substrate generating plasma by high voltage discharging supplying reactive gas to a polymerizing chamber and strengthening the characteristic of the surface of the substrate generating plasma by high voltage discharging and supplying mixed gas of oxygen and nitrogen to improve and maintain hydrophile of a surface of a substrate deposited with polymer by polymerizing processing the present invention can strengthen surface processing and surface processing characteristic of the substrate by supplying the reactive gas and unreactive gas in order in the system composed of one chamber the reactive gas and unreactive gas is supplied to separate chambers in a system having a number of chambers and the polymerizing step and strengthening step are performed in order on the path where the substrate moves the plasma polymerizing system is comprised of an electrode installed in the chamber reactive gas supplied into the chamber a polymerizing chamber having the substrate surface coated by plasma discharging and positioned opposite to the electrode an electrode installed in the chamber mixed gas of oxygen and nitrogen so that the surface coated substrate maintains the characteristic and a strengthening chamber arranged opposite to the electrode it is desirable that the substrate is polymerized.