The present invention relates to, for example, an image pickup system having a structure capable of imaging a subject at a low power consumption and a low cost even when the subject may be dark. The image pickup system comprises an image pickup device, a peak position detecting section, a partial image acquiring section, and a partial image operating section. The image pickup device outputs image data that represents the two-dimensional intensity distribution of light incident on a photodetecting section, and outputs light intensity profile data that represents the one-dimensional intensity distribution of the incident light in each of first and second directions in the photodetecting section. The peak position detecting section detects a light intensity peak position in the two-dimensional intensity distribution of the light incident on the photodetecting section in the image pickup device, based on the light intensity profile data outputted from the image pickup device. The partial image acquiring section acquires a partial image from an entire image that can be imaged by the image pickup device so that the light intensity peak position detected by the peak position detecting section is made a specific position for the partial image in the entire image. The partial image operating section integrates the acquired partial image.