Abstract: A moving body comprises two members interconnected by a flexible linear member and each symmetrical with respect to a plane perpendicular to the direction of its movement through a pipe. The moving members are congruent with each other and are preferably made of an elastic material. Work is performed in the interior of pipes, for example, for lining with use of the moving body by applying a fluid pressure to the back side of the body. As a preferred example of lining work, the moving body is used for reforming an outworn underground pipe by lining the pipe with a resin layer having strength to withstand an external pressure of at least about 0.1 kg/cm.sup.2 G per meter of the depth at which the pipe is laid underground. The pipe is used as a frame for this operation.