For each pixel read from an imaging device, a horizontal counter value and a vertical counter value corresponding to the pixel are supplied from a signal generator to a distance computation section via an optical-axis-center coordinate setting section and an up-and-down and right-and-left weighting section. In the distance computation section, the distance to the optical-axis center is computed, and correction coefficients for the zoom wide end and for the zoom tele end, which correspond to the distance, are obtained by look-up tables. The two obtained correction coefficients are blended at a mixture ratio determined by a blend ratio setting section. The blended shading correction coefficients are gain adjusted by a gain adjustment section, after which they are supplied to a correction section. As a result, a correction corresponding to the distance to the optical-axis-center position is performed on the signal of each pixel supplied from an imaging section.