To reduce variation in luminance among a plurality of output images.

A pixel value correction means 12 corrects the value of each pixel so that representative luminance is included in a prescribed range for respective acquired images for a plurality of continuously captured images in a time series. After that, a luminance change rate determination means 140 determines whether a rate of change in luminance of the representative luminance deviates from a prescribed range, and a periodical variation determination means 141 determines whether temporal variation in the representative luminance is periodical or irregular. A processing means 16 for irregular variation smoothes the acquired image by an already acquired image when the rate of change in luminance deviates from a prescribed range or when it is determined that temporal variation of the representative luminance is irregular. When it is determined that temporal variation of the representative luminance is periodical, a processing means 15 for periodical variation extracts one prescribed acquired image or a plurality of acquired images to generate output images in synchronization with the period of a processing term in the plurality of acquired images included in the processing term that is an integer multiple of the time variation period of the representative luminance.