The guide device described includes guide elements (2, 3, 4, 5) mounted on each other in pairs, one being designed as a guide rail (2, 3) for the second (4, 5), plus a measurement unit (30, 50) with two measurement elements working in conjunction with each other to monitor the relative motion of the guide elements. A first measurement element is designed as an incorporated scale (30) and mounted on the first guide element (3). The second measurement element is designed as a measurement head (50) and works in conjunction with the scale (30). The guide rail includes a multiplicity of guide surfaces of which at least a first surface (39) is intended to support the second guide element (5) and a second surface (38) is designed to incorporate the scale (30). The measurement head (50) is mounted on the second guide element (5). The scale (30) can be fitted directly on the second guide surface or it can be fitted on/in the material of a lengthwise support and the support mounted on the second guide surface. The guide device can be designed as a single-rail system or both guide elements can be designed as guide rails mounted on each other. Transmission of the signals from the measurement head to a switch unit can be carried out optically.