An image processing technique that enables accurate detection of a flicker component even when applied to an image pickup device capable of changing a driving method on a region basis within a frame. A flicker detection section detects a flicker component of an image pixel signal read out from the image pickup device having a pixel region for detecting a phase difference. When the driving method is changed to one for performing phase difference detection, the flicker detection section detects a flicker component such that the period of the flicker component in a region used for phase difference detection within the frame coincides with a period of the flicker component in a region not used for phase difference detection.