To provide a machining device guide rail easily manufactured at low costs, light in weight, easily used and easily adapted to have a length needed by a user.

A guide rail 1 used for a machining device for machining a base material such as a stone or the like, for example for a crown drill, is provided with guiding surfaces 9, 10, 11 and 12 extended toward the longitudinal direction of the guide rail so as to guide/support a machining device housing, and a profile portion 13 extended in parallel with the guiding surfaces 9, 10, 11 and 12. The profile portion 13 is composed of a series of engaging edge parts 14 and 15 disposed at regular intervals and extended in the width direction of the guide rail 1. The guide rail 2 is made of a shape 2 prepared by press- bending a long metallic sheet element. The guiding surfaces 9, 10, 11 and 12 engaged with the feeding means of the machining device side and the profile portion 13 are integrally disposed in the shape 2.