PURPOSE: To simplify constitution, and realize diametric reduction and downsizing by arranging two elastic expansible bodies, which expand in the diameter direction by pressurization and are locked on a wall surface in a pipe line, continuously in the diameter direction of the pipe line, and arranging an elongation regulating body in one elastic expansible body.

CONSTITUTION: Elastic expansible bodies 4 and 5 to be locked on a wall surface in a pipe line expanding by pressurization, are arranged continuously in the shaft direction of the pipe line in a self-traveling device body 3. Fiber 13 as elongation regulating body to regulate shaft directional elongation caused by the pressurization is arranged in the expansible body 4. When the expansible body 4 is pressurized, it expands in the diameter direction, and contracts in the shaft direction by an action of the fiber 13. At this time, the body 3 is locked on an inside surface of the pipe line. In succession, the elastic expansible body 5 is pressurized, and the body 3 is locked on the inside surface of the pipe line by the expansion. After this expansible body 5 is locked, the expansible body 4 returns to an initial condition after the pressurization is stopped. At this time, since the expansible body 5 is locked on and fixed to the inside surface of the pipe line, the expansible body 4 elongates in the axis direction with a locking and fixing part as its center, and the body 3 moves in the shaft direction.