PURPOSE: To perform prealignment of improved accuracy over a wide range in a relatively short time and reduce time required for positioning by prealigning a mark for alignment and an auxiliary mark constituting a mark for detecting position by scanning using light or particle beams.

CONSTITUTION: If positional deviation before scanning is within the total range 21k where a mark for detecting position is placed when a diffraction grid of auxiliary marks B1, B2, and B3 and that of auxiliary marks C1, C2, and C3 are placed at specified gap at left and right of diffraction grid of mark A for alignment when scanning a diffraction grid 4 by incident light by moving either a wafer 2 having the diffraction grid 4 or incident light, two or more peaks of signal by diffraction light can be observed by scanning a distance which is slightly longer than maximum gap of adjacent marks for detecting position, namely, the gap 6k between the auxiliary mark C2 and the auxiliary mark C3. Then, from the two peak positions and peak gap among two or more peaks, it becomes possible to know a rough position of diffraction grid of the mark A for alignment highly accurately and easily.