Abstract: A truing apparatus for an angle grinding wheel with two grinding surfaces is provided with an AE sensor for detecting the contact of a truing tool with each of the grinding surfaces. The truing tool is provided on a follow slide which is mounted on a traverse slide. As the traverse slide is moved in a first direction, the follow slide is moved following a template in a second direction extending across the first direction. In response to a truing command, at each of first and second traverse positions in the first direction, the truing tool is advanced relative to the follow slide until a contact signal is issued from the AE sensor upon contact of the truing tool with a corresponding one of first and second grinding surfaces. A position sensor detects first and second feed positions at which the truing tool contacts the two grinding surfaces. One of the feed positions which is shorter in distance from the follow slide is selected to determine a truing start position.