PURPOSE: To secure the large space for work in the rear part and incorporate segments free from hindrance even in the case of a noncircular miscellaneous diameter tunnel, by installing an advance mechanism which can be installed separately from a shield machine, does not require a rail, etc., and is free from the obstruction in other work.

CONSTITUTION: On a device body 12 having the outer periphery 12a in slide contact with the inner periphery of an assembled segment 11, propulsion jack 14 engaged with the segment 11 is installed, and a housing 26 is installed in a laterally shiftable manner on the device body 12. An arm 18 is incorporated on the housing 26 in a turnable and longitudinally shiftable manner, and a segment holding mechanism 25 which supports the end part of a rod 23 having a segment catching part 22 at the center, by two jacks 24a, is installed at the top end of the arm 18.