An object of this invention is to suppress both the influence of a change in image quality by flicker and the influence of degradation of the image quality by a camera shake when an electronic still camera takes a picture under illumination having flicker. In an electronic still camera which captures a plurality of low-luminance images and composites them into one image of correct exposure, when the exposure time is shorter than the flicker interval of illumination light, the center of the exposure time is made to substantially coincide with the maximum value of the light quantity of illumination light. When the exposure time is longer than the flicker interval of illumination light, the exposure time is set again to a natural number multiple of the flicker interval.