To easily check whether or not segments for shield segment construction are surely connected to each other by means of a one-touch joint from the outside of the segment.

The segment joint comprises a pipe body 2 which is fixed to the connecting surface of one segment 1A, a claw member 9 which can protrude from/recede into the pipe body 2, and a joint hole 5 which is formed at the connecting surface of the other segment 1B and into which the pipe body 2 is inserted. When the pipe body 2 is inserted into the joint hole 5, the engaging surface 9A of the claw member 9 which is protruded from the pipe body 2 is engaged with the backside of the connecting surface of the other segment 1B, so that both the segments 1A and 1B can be connected to each other. A cable insertion hole 10 ranging from the outside of one segment 1A to the pipe body 2 is formed at one segment 1A; an optical fiber cable 11 is inserted into the cable insertion hole 10; light is applied into the pipe body 2 from the optical fiber cable 11; and the state of connection between both the segments 1A and 1B is checked according to reflected light from the engaging surface 9A.