PURPOSE: To decrease surface defects by roll marks by controlling the volatile matter concn. Cb of the coating liquid in a heating atmosphere in such a manner that the concn. Cb in the heating atmosphere in the initial period of heating and drying and the volatile matter saturation concn. Cw in the coating film on the surface of a band- shaped body attain Cw<Cb.

CONSTITUTION: The heating up of the coating film surface is possible without generating evaporation and the leveling is accelerated by the viscosity drop during this period if the volatile matter concn. Cb of the coating liquid in the heating atmosphere and the volatile matter saturation concn. Cw in the coating film corresponding to the coating film temp. on the surface of the band-shaped body are so controlled as to attain Cw<Cb in order to heat up the coated surface and to lower the viscosity while suppressing the evaporation from the coating film surface in the initial period of heating. The volatile matter concn. Cb of the coating liquid in the heating atmosphere is measured in an initial period zone 61 of a drying furnace 6. The coating film temp. on the long surface of the band-shaped material 1 is simultaneously measured and the volatile matter saturation concn. Cw in the coating film is determined. A control signal is sent to a concn. controller 8 in such a manner that both concn. Cb, Cw attain Cw<Cb. The concn. Cb in the heating atmosphere in the furnace is controlled to Cb<Cw by a controller 81 provided in the initial period zone 61 therefrom.