PURPOSE: To continuously form an optimum thin film exhibiting high electric conductivity and transparency by measuring the resistance value of the thin film formed on a substrate in plural regions in the cross direction, and independently controlling the gas supply amt. from plural gas inlet pipes based on the respective measured values.

CONSTITUTION: When a film rewound from a rewinding roll 2 passes a main roll 3 in a vacuum vessel 1, an electric discharge is generated in the atmosphere of the gaseous mixture of an inert gas and an active gas, and the metallic substance of a target 6 is allowed to react with the active gas to form a thin film on the film. The sheet resistivity of the thin metal oxide film thus formed on the film is sent to an arithmetic unit 9 by a rotary electrode 4. The sheet resistivity is compared with a preset reference value, and a gas flow rate controller 10 is controlled based on the difference. By this method, the supply amts. of the inert gas and active gas flowing in gas inlet pipes 5(5AW5D) are independently controlled by the gas flow rate controller 10.