To perform a rigidity test of a segment ring accurately and efficiently.

A plurality of arcuate segments 1 are jointed together in circumferential direction to assemble into annular shape, thus a segment ring is formed. A PC steel wire 11 is attached by winding circumferentially from an outer peripheral side while a PC steel rod 15 is attached by penetrating radially from one side of the outer peripheral side to the other. On inner peripheral side of the segment ring, a length measuring device 18 is radially provided while an angle measuring device 19 is so provided as to bridge the two jointed segments 1. The PC steel wire 11 is tensioned by a hydraulic jack 14, while the PC steel rod 15 is tensioned by a hydraulic jack 17 to apply specified axial- tension and load in circumferential and radial directions of the segment ring. The displacement of inside diameter of the entire almost-annular segment ring is measured by the length measuring device 18 while the displacement in angle of a coupler part of the segment 1 is measured by the angle measuring device 19.