PURPOSE: To enhance operability and functionability in a wide range and improve an outside appearance by enabling a ladder to move sliding along a support bar which is slidable in the crosswise direction and used as a supporter in structure. CONSTITUTION: A pair of support bars 2'a and 2'b installed inside a pair of base bars 2a and 2b supported on stays 1a and 1d mounted on a car loop are adapted to be slidable along two joint bars constructed on the base bars and arranged to support in a state which allows the joint bars to be penetrated into the lower part of the support bar 15a or the like, thereby fixing their spacing with two inside bars 16 or the like. A double-leg ladder is formed in such a fashion that a projection 4a or the like outside posts 5a and 5b may be fitted in a groove 36 or the like installed inside the support bars. A handle 7a or the like mounted on steps 8a or 8d are turned upward in the outside direction when using this ladder. Since two projections on one side of the ladder are designed to be pulled into a post being interlocked with the turning of the handle, they are released from the grooves, it is possible to move the ladder slidingly by two projections installed on the opposite side to the released side.