The invention relates to a machine tool, especially a diamond drill. Said machine tool comprises a rotatably driven spindle (11) having an end section (111) supporting an external thread (14), a tool (12), especially a drill bit, having a hollow-cylindrical tool shank (16) with an interior thread (15), to be screwed onto the spindle end section (111), and a release device (13) disposed between the tool shank (16) and the spindle (11). For an easy handling of the release device (13) without tools, the release device is captivated to the spindle (11) and comprises a supporting ring (21) fastened on the spindle (11), and a supporting ring (22) seated on the spindle (11) at a distance from the first supporting ring and being axially displaceable to a limited extent. Said supporting ring is fastened on the other supporting ring (21) in a rotationally fixed manner and is supported on a face of the tool shank (16). A manually rotatable selector ring (23) engages between the supporting rings (21, 22) and allows to change the clearance between the supporting rings (21, 22).