An image processing apparatus can detect a predetermined target object from image data. The image processing apparatus includes an image zooming unit configured to generate a plurality of pieces of zoomed image data that are mutually different in magnification from the image data input by an image inputting unit, a detection unit configured to extract a partial area from the plurality of pieces of zoomed image data generated by the image zooming unit, and detect the predetermined target object by performing collation to determine whether the extracted partial area coincides with a detection pattern stored in a detected pattern storage unit, and a detected information storage unit configured to store detection information including magnification information of the zoomed image data from which the predetermined target object is detected by the detection unit. In a case where the detection information is stored in the detected information storage unit, the image zooming unit determines a magnification of the zoomed image data based on the detection information and generates at least one piece of zoomed image data whose total number is smaller compared to a case where the detection information is not stored.