PURPOSE: To improve rectilinear moving property and prevent vibration by providing recessed parts on the inner faces in the front and rear direction of end cap parts, providing guide parts connected to the recessed parts of the end cap parts on the inner faces in the front and rear direction of the middle parts of a moving body, and forming guide grooves to connect the outward trip and the return trip of rolling elements out of the recessed parts and the guide parts.

CONSTITUTION: A moving body 2 is constituted of end cap parts 4 and a middle part 5, and the respective parts 4, 5 are formed with leg-shaped parts 6, 7. Circular-arc-like recessed parts 17 are formed on the inside faces in the front and rear direction of the end cap parts 4. On the inner circumferential faces of the recessed parts 17, ball guide grooves 19 connected to the ball guide grooves 11 of ball outward trip 12 are formed. Meanwhile, semi-columnar guide parts 23 are formed on the front and rear both ends of the leg-shaped parts 7 of the middle part 5, and ball guide grooves 11 and ball guide grooves 20 of ball return trip 13 are formed. When the end cap parts 4 and the middle part 5 arc joined together, reversal passages 14 are formed out of the ball guide parts 23 and the ball guide grooves 19.