To provide a runner, having a cantilever supporting structure with a derailment preventing function, saving labor required for the execution of work for a sliding door and reducing the cost of the execution by allowing a completed door panel, whereto the runner and the like are assembled, to be easily suspended on a guide rail.

The runner 7 is composed of a runner body 12, having a cantilever structure and suspended on the guide rail 2, and a mounting part 13 fixed to a door frame 5. The runner body 12 is composed of a suspension shaft 20 and a roller 21, rotatably supported by the suspension shaft 20, which is supported by the holder 23 of the mounting part 13. The upper part of the holder 23 is provided with a derailment-preventing body 38 for preventing derailment of the roller 21. The body 38 can slide between a regulating position, where a regulating surface 38a at the upper end of the body 38 faces the lower surface of the guide rail 2 and a suspending position, where the regulating surface 38a is moved away from the guide rail 2. The door panel 4 is suspended with the body 38 being retracted in the suspending position.