An image processing apparatus which is capable of suppressing an increase in the circuit size of buffers between data-processing circuits, thereby enabling an associated component thereof to be implemented by hardware. A position control unit sequentially shifts a position of a sub window image by a predetermined skip amount in a predetermined scanning direction, for scanning, and further repeating the scanning for skipped sub window images, after shifting a start position of the scanning, to thereby determine positions of all sub window images each as an area from a face image is to be detected.