In a thin film coating method, tack members are brought close to a surface of a substrate to temporarily tack the forward end portion of a web of thin film to the forward end of the substrate. Compression-bonding rollers are then brought into a tacking position where the forward end portion of the thin film is tacked from a standby position where the compression-bonding rollers do not touch the tack members to make compression-bonding contact with the forward end portion of the tacked thin film after the tack members are moved away from the surface of the substrate. The compression-bonding rollers are then rotated at the tacking position for the double purpose of conveying the substrate and adhering the thin film to the substrate. In this process, the forward end of the substrate is detected to produce a detection signal at a detection position before the substrate is conveyed to the tacking position, the conveyance of the substrate is stopped after the forward end of the substrate has been conveyed from the detection position to the tacking position, and the tack members are brought close to the conveyance passage of the substrate while the forward end of the substrate is being conveyed from the detection position to the tacking position to thereby tack the forward end of the thin film to the surface of the substrate after the forward end of the substrate is stopped at the tacking position.