An image pickup apparatus includes an image pickup element configured to provide a photoelectric conversion to an optical image formed by an image pickup optical system, a correlation image acquirer configured to obtain a product between a pixel value of an image output from the image pickup element and a representative value of a reference signal that fluctuates during an exposure time period for each of a plurality of divided time periods made by dividing the exposure time period by a predetermined division number, and a correlation image calculator configured to obtain an output from the image pickup element and to calculate a sum of the product for the exposure time period as a correlation image.