To provide an adjusting method of a branched imaging mechanism which adjusts highly accurately positions of a plurality of branched phase shift interference fringes imaged by different imaging mechanisms.

This method comprises a first adjusting means for imparting separately an optical phase difference to a sample light optical axis, and a second adjusting means for imparting separately an optical phase difference equivalent to the case where an inspection face capable of imaging an interference fringe is tilted to the sample light optical axis. A first fixed optical phase difference by the relative difference of numerical data at a positional temporary corresponding point is determined by the first adjusting means. The optical phase difference is imparted separately by the second adjusting means, and a second fixed optical phase difference by the relative difference of the numerical data at the temporary corresponding point is determined by the second adjusting means. The branched imaging mechanism is arranged and adjusted on the face approximately orthogonal to a branched original beam so that specific positions in an inspection face observation range are on the same position in each branched observation coordinate system by using the positional difference calculated from the relation between the first fixed optical phase difference and the second fixed optical phase difference.