PURPOSE: To shift a frame in an optimum removed condition in accordance with a curved state or others of a tunnel, by deforming an invert form in various manners.

CONSTITUTION: In shielding frames 1 of a tunnel provided with an invert form 8 between the ends 2a, 3a of a pair of side forms 2, 3, the both ends 8a, 8b of the invert form 8 and the ends 2a, 3a of both side forms 2, 3 are formed to be butt-jointed respectively. Hinge brackets 11a, 11b and 12, 13 to detachably fit a hinge pin 10 for deformably and rotatably attaching the invert form against respective both side forms, are respectively provided at both ends 8a, 8b of the invert form and the ends 2a, 3a of both side forms.