To solve the problem that nonuniform illumination intensity and resolution degradation cannot be avoided as an imaging element is further reduced in size and further increased in the number of pixels.
An ND filter, which has a plurality of density areas differing in light transmissivity in the moving direction of the light shield blade, is attached to this light shield blade. The light shield blade is driven to be opened only in an opening side rather than in a limit aperture diameter, which is set between two positions. One of the position is such that the area of a light passage opening covered with the lowest-light-transmissivity density area of the plurality of density areas of the ND filter is largest in the entire light passage opening. The other one is such that the area of the light passage opening covered with the lowest-light-transmissivity density area of the plurality of density areas of the ND filter is zero in the entire light passage opening. A shutter speed when it is determined that the light passage opening set to the limit aperture diameter is subjected to over-exposure is made higher than the shutter speed used when the light passage opening is set larger than the limit aperture opening.