1. A film thickness measurement apparatus configured to measure a film thickness of a film formed on a substrate, the film thickness measurement apparatus comprising: an imaging device that images a front surface of the substrate; a measured value storage part that stores a plurality of film thickness measured values obtained by measurement in advance at a plurality of coordinates on a measurement preparation substrate and coordinates corresponding to the film thickness measured values, for a film formed on the measurement preparation substrate and having a non-uniform thickness; an image storage part that stores a preparation imaged image obtained by imaging the measurement preparation substrate in advance by the imaging device; a pixel value extraction part that extracts a pixel value at each coordinates stored in the measured value storage part from the preparation imaged image stored in the image storage part; a correlation data generation part that extracts, from the measured value storage part, the film thickness measured value at each coordinates corresponding to the extracted pixel value, and generates correlation data between the extracted film thickness measured value and the extracted pixel value; and a film thickness calculation part that calculates a film thickness of a film formed on a substrate being a film thickness measurement object on a basis of a pixel value of an imaged image of the substrate being the film thickness measurement object and the correlation data generated in the correlation data generation part.