Abstract: A web is fed from a feeder to a leveling treatment chamber. The web is heated with heating rollers in the temperature range of 50 to 125° C. provided in the heating zone of the leveling treatment chamber. In this heating operation, warm air in the temperature range of 30 to 125° C. is blown from a warm air fan into the heating zone. Then the web is fed to the cooling zone of the leveling treatment chamber and cooled with cooling rollers. The temperature of the cooing rollers is controlled with a temperature controller while measuring the surface temperature of the web with a temperature sensor placed downstream relative to the leveling treatment chamber. Controlling the temperature of the web before the coating operation to 25 to 45° C. enables the surface of the web to be leveled, thereby enabling an excellent coating film to be formed with a coating apparatus.