PURPOSE: To widen the effective inside diameter of an erector by a method in which a pair of left and right-handed strut segments to be set between the upper and lower contacts between one of cylindrical cross sections and both-side cylindrical cross sections, which are arranged in parallel in a multiple shield tunnel are assembled by only one erector.

CONSTITUTION: On the same erector rings 2, two sets of one-arm type hang beams 4A and 4B slidably supported through guide rods 7A and 7B by arms 3A and 3B provided on one side of an erector ring 2, each having segment holders 5A and 5B, are provided. The beams 4A and 4B are arranged in such a way as to almost orthogonally cross the rods 7A and 7B. One-side strut segment PA is assembled by the first hang beam 4A, and the opposite-side strut segment PB is assembles by the second hang beam 4B in a separated manner.