A bevel unit comprises CCDs and processing liquid nozzles, and the CCDs take an image of a circumferential edge surface of a substrate. An image processing part detects the distances between the circumferential edge surface of the substrate and the processing liquid nozzles by image processing the signals from the CCDs. A control unit compares thus detected distances between the circumferential edge surface of the substrate and the processing liquid nozzles with set distances from the circumferential edge surface of the substrate to the processing liquid nozzles which are set in a recipe so as to be a desired rim etching width, and calculates an amount of displacement between the detected distances and the set distances. In accordance with the amount of displacement, the control unit activates motors and accordingly positions the bevel unit.