PURPOSE: To achieve simplification of the structure of a guide arm by forming a clearance on the fitted part of a linear guide rail and the engagement arm of a linear guide for which a groove to be fitted into the protrusion of the guide rail, and by introducing a lubricating oil to the clearance so as to form an oil film.

CONSTITUTION: A protrusion 2a of roughly Y-shaped cross section, is formed in an integrated way on the upper part of a linear guide rail 2 mounted and fixed on/to a main body 1. Guide arms 8, 9 of a linear guide 3 are mounted by. mounting bolts 12, 13 in such a way that the protrusion 2a is sandwiched therebetween. Since the guide arms 8, 9 are formed in a divided way, the shape thereof can be simplified. A clearance is formed between the protrusion 2a and the linear guide 3, and a lubricating oil is supplied from passages 19a, 19b, 19c, and sliding is facilitated since an oil film is formed on the clearance. In this structure, the shape of the guide arms 8, 9 is simplified, and manufacturing efficiency is thus improved.