Abstract: A dressing device capable of effectively performing, in a centerless grinding machine, dressing to a grinding face of a grinding wheel and a rotary supporting face of a regulating wheel, performing relative positioning in axial direction of the grinding wheel and the regulating wheel after dressing, easily and accurately, and also reducing the equipment installation space. The dressing device includes a single dressing means for performing dressing to the grinding face of the grinding wheel and the rotary supporting face of the regulating wheel, this dressing structure including a rotary dresser having a profile fit for the grinding face of grinding wheel and the rotary supporting face of the regulating wheel.