The present invention relates to a portable grinding tool, in particular to a super-precision grinding machine (10), comprising a casing (12), a bearing part (14) of grinding plate and a plurality of retaining devices (20, 23; 340, 500) used for fixing the grinding plates (16, 150) on the bearing part (14) of grinding plate, more particularly for fixing the ends of the grinding plates (17, 19, 155) at opposite ends. In order to operate more simply, fast and reliably, the invention is characterized in that the retaining devices (20, 23; 340, 500) can be set active and/or inactive together via a single operation device (35; 350) to loosen or tighten the grinding plate (16).