※ This following Abstract Information is not including formula and image information. If you want to know these information, Check the Full Text infromation Please. Precision well estimates the film thickness based on the reflection light from the substrate. As to the rotation period which the film thickness estimation method according to one side of the disclosure rotates on the surface to form the film of the processing liquid, the film thickness estimation method according to one side of the disclosure includes the light is irradiated to the place overlapped with the surface of the substrate, the light, the reflection light, the measurement point of time when being determined of the rotation within period among the signal waveform, the feature amount is acquired from the waveform between the point of time when satisfying the condition that the signal waveform is determined as to the measurement view point move, and the thickness of the film of the processing liquid in the measurement point of time is produced based on the feature amount acquired. The light interposes the film of the processing liquid after the surface is reflected and comes the surface of the substrate out. As to the reflection light, the light reflected in the warped surface of the film of the processing liquid is synthesized light is received. In that way the signal waveform showing the time variation of the intensity of the reflection light in the rotation period is acquired.