A regulating wheel dressing system in a centerless grinder, having a dressing tool for dressing a regulating wheel, which dressing tool is adapted to be feed-controlled in a direction parallel to the axis of rotation of the regulating wheel and also in a crossing direction by a feed control means, which in turn is controlled biaxially simultaneously by a control means. Coordinate values of plural points on a rotated hyperboloid of one sheet of revolution to be formed on the regulating wheel are calculated and the dressing tool is feed-controlled for coordinate interpolation between the plural points with those coordinate values as target points. The regulating wheel can be dressed to the rotated hyperboloid of one sheet of revolution in high accuracy independently of changes of its diameter and even where it is stepped for supporting a stepped work.