The processing apparatus 3 includes an extracting unit 33e, an estimation unit 33f, and a difference calculation unit 33g. The extracting unit 33e extracts a first image signal generated by pixels that have received light of a first wavelength band and a second image signal generated by pixels that have received light of a second wavelength band different from the first wavelength band, from an image signal of one frame captured by imaging an object when the object is irradiated with light of the first wavelength band. The extracting unit 33e estimates an image signal to be generated by a pixel that has received the light of the second wavelength band based on the first image signal extracted by the extracting unit 33e. The difference calculation unit 33g obtains a differential image signal by calculating a difference, on a corresponding image portion, between the second image signal extracted by the extracting unit 33e and the image signal estimated by the estimation unit 33f.
