PURPOSE: To improve detection responsiveness and accuracy by detecting the spacial positions of images from correlations of two sets of random patterns.

CONSTITUTION: The image light through two-dimensional random patterns 13, 15 such as of grating form slits or the like of 1:1 in the ratio of the transparent part and non-transparent part corresponding to the image 12 such as of a microfilm or the like passes through both patterns 13, 15 only when the both patterns 13, 15 align and is then detected with a photo sensor 16. Hence, the detection signal ratio of the sensor 16 at the aligning of the both patterns 13, 15 and immediate therebefore increases, due to which the detection responsiveness and detection accuracy of the images improve. When a stepping motor 21 is controlled by the detection signal of the sensor 16, the images of the film 12 may be stopped in the specified position at high speed and high accuracy.