An image pickup device and associated methodology are provided. The image pickup device is formed from a plurality of pixels, each of which can perform any of an exposure operation and a reading operation thereof at a timing different from that of the other, an imaging apparatus is provided, which can determine the amount of main-flashing light based on pre-flashing by a flash highly accurately. Before and during a preflash operation by a flash unit, an exposure operation is started simultaneously for all the pixels of the image pickup device 14 to form an image before and during the preflash to obtain a detected value by a detector before and during the preflash, respectively. A computation circuit computes a differential detected value obtained by subtracting the before-preflash detected value from the during-preflash detected value. The differential detected value is a detected value containing only pre-flashed light with ambient light excluded. An amount of light for main flashing is computed on the basis of the differential detected value.