To form a film having uniform thickness on a disk substrate by a spin coat method.

When a thin film is formed by using the spin coat method on the surface of the disk substrate 10 having a circular aperture 10a formed at the center thereof and fitting to a spindle of a disk substrate, the aperture 10a provided at the center of the disk substrate 10 is closed by sticking a sticker 12 to the disk substrate. A prescribed amount of e.g. a UV curable resin is dropped onto the center of the sticker 12, that is, the center of the disk substrate 10 and then the disk substrate 10 is rotated to form the thin film on the surface of the disk substrate 10.