PURPOSE: To prevent cutting chips, etc. from infiltrating without requiring a special space to house a cover by covering and protecting the guide surface with a flexible plate-like body having a spring force and providing a space penetrating the plate-like body on the mobile member side mounted with a tool box.

CONSTITUTION: A rolling element 33 mounted and fixed with a tool box 32 on the upper surface and having balls in contact with a rail 22 on the surface is provided on a mobile member 31. A plate-like body 40 having a spring force is provided on the guide surface of a support member 21 supporting the mobile member 31, a space 34 capable of penetrating the plate-like body 40 relatively movably is provided on the mobile member 31 to penetrate the plate-like body 40 through the space 34 and to fix both ends to the support member 21. A recessed section 24 housing a drive screw 25 and a nut 26 moving the mobile member 31 is provided inside the rail 22. The plate-like body 40 covers the rolling element 33 above the support member 21 and protects the rail 22 from cutting chips, etc. by being in close contact with a guide plate 23 in the front.