1. An imaging device comprising: a single photographing optical system; an image sensor having a plurality of pixels for obtaining a plurality of viewpoint images by photo-electrically converting a luminous flux passing through different regions of the photographing optical system; and a shading correction part for conducting a shading correction to the plurality of viewpoint images, and the shading correction part varies the amount of shading correction based on light-reduction property for one viewpoint image among the plurality of viewpoint images with respect to the amount of shading correction based on light-reduction property for the other viewpoint image among the plurality of viewpoint images.