An image processing apparatus capable of highly accurately detecting and correcting color shift of image data, caused by a chromatic difference of magnification. The image processing apparatus stores first color shift amount data including color shift amount information of the image data and accuracy information indicative of detection accuracy of the color shift. The image processing apparatus analyzes the image data to thereby determine second color shift amount data including color shift amount information of the image data and accuracy information indicative of detection accuracy of the color shift. The image processing apparatus corrects the color shift of the image data using the color shift amount information selected from the first and color shift amount data, based on the accuracy information included in the first color shift amount data and the accuracy information included in the second color shift amount data.