PURPOSE: To make unattended the work in a shaft to eliminate danger by operating segment assembling arms so that they are alternately arranged up and down, holding segments respectively to descend the inside of the shaft, and assembling segments for one ring at a time.

CONSTITUTION: Segments for two rings 8... are arranged to the circumferential edge of a shaft port, upper step arms 9d, 9e and 9f are extended, the segments 8... are held to reduce, and the segments 8... are held by lower step arms 9a, 9b and 9c to reduce. After that, the segments are lowered right above a shield excavator 6, the arms 9a - 9f are extended to make pressure-welding to a tail plate 46, and the segments 8... for one ring are temporarily assembled. Shield jacks 47... are extended to fix the segments 8..., and they are fastened to existing segments 48.... According to the constitution, the segments 8... require no carrying facility and transferring work, and work can be efficient.