PURPOSE: To embody the rationalization in execution, by installing a tightening mechanism inside and permitting the automatic tightening by the tightening mechanism after arrangement.

CONSTITUTION: As for a segment 6 which is constituted so that a screw socket is arranged on one of the joint surfaces 6b in the tunnel circumferential direction, and a tightening bolt 9 screwed with the screw socket is arranged on the other, and a long tightening bolt 10 as rotary driving shaft is arranged in the between-ring joint direction in the segment 6. The tightening bolt 9 is arranged in the joint surface 6, and further, a rotary sending-out mechanism for bolt is installed. Further, the long tightening bolt 10 and the rotary sending- out mechanism 12 are interlocked by a transmission mechanism in the combination of gears, chains, sprockets, etc.