PURPOSE: To eliminate the misalignment of each rail, to facilitate the assembly and to make the containing space small by connecting one end of a roughly circular arc-like connecting rail formed in a connecting body to a going-motion rail, and connecting the other end to a return-motion rail.

CONSTITUTION: The upper and the lower chambers 20, 21 in the upper rail 8 are formed consecutively, and also, on a substrate 3, a square hole member 39 is formed, a connecting bar 42 of an intermediate connecting tool 41 is inserted through a square hole 40 of this square hole member 39, an a semicircular arc part 42 of the intermediate connecting tool 41 is inserted through the lower face of the upper piece 43 of a connecting body 5, and the connecting body 5 is connected to the upper rail 8 through the intermediate connecting tool 41. In such a case, a horizontal roller 16 of the upper runner 13 is subjected to swing stop by the square hole member 39 and a rail side wall 44. A going- motion rail 1 and a return-motion rail 2 are held in a common substrate 3, misalignment of the going/return motion rails 1, 2 is suppressed, an interval between the going-motion rail 1 and the return-motion rail 2 is narrowed, and occupied space of an endless rail is made small, and the containing space is made small.