To provide a method for detecting a shift of an image when an image process for a general document is performed.

An image reduction part 1 generates a reduced image S1 of an image A. A lateral black run histogram generation part 2 generates a lateral black run histogram S2. A rough longitudinal feature extraction part 4 extracts a rough longitudinal feature quantity S4. A fine longitudinal feature extraction part 6 extracts a fine longitudinal feature quantity S6. Similarly, a rough lateral feature quantity S5 and a fine lateral feature quantity S7 are extracted. A position feature quantity recording part 8 records the rough longitudinal feature quantity S4, fine longitudinal feature quantity S6, rough lateral feature quantity S5, and fine lateral feature quantity S7. The image reduction part 11 generates a reduced image S11 of an image B. A lateral black run histogram generation part 12 generates a lateral black run histogram S12. A longitudinal shift temporary detection part 14 generates a temporarily detected value S14 of the longitudinal shift. A longitudinal shift detection part 16 outputs the detected value S16 of the longitudinal shift. Similarly, the detected value S17 of the lateral shift between the images A and B is outputted from a lateral shift detection part 17.