To provide a method and an apparatus for continuously measuring a thickness of an extremely thin ceramic film in a non-contact manner with a high speed.

The apparatus is constructed by assembling a main body scanning and measuring a thickness of a film in a film manufacturing line, a notebook computer for operation and displaying, and a power/communication regions box. The thickness of an extremely thin ceramic film is measured by throwing an illumination with a floodlight source angled at a certain angle towards the axis of measurement, measuring only an intensity of transmission diffusion emittance without measuring a rate of transmission attenuation of the light directly, and utilizing a difference of the transmission diffusion emittance according to a transmission wavelength and a thickness.