In machine tool control, it is known that using the contour errors which are defined as tracking error component orthogonal to desired contour curves, as feedback signals is effective for precision contouring. Since the exact feed drive dynamics must be known in the conventional contouring controller design, we propose a design of robust contouring control system in this paper. We firstly introduce a controller design by which we can assign the controller gain for reducing the contour error independent of tangential error component to the desired contour curves. A robust contouring controller is then designed based on the variable structure control. The effectiveness of the robust controller is demonstrated by experimental results.