A truing tool for a grindstone (1) is intended for attachment to a universal support (3) of a grinding machine in parallel with the rotation axis of the grindstone. It has - in a holder (12) therefore - a cutting tip (13) for truing engagement with the grindstone. The holder (12) is movably connected to a yoke (10) - to be attached to the universal support (3) - by externally operated means (14, 15) on the yoke for its movement in relation to the yoke transversely of the grindstone (1).