Device for the machining of a workpiece in a clamping fixture by using tools (WZ) which can be taken in alternating sequence from a tool magazine with sequence control of the machining steps, with a tool spindle unit changing device (14) consisting of a movable, rotatable and pivotable clamp (ZQ), the jaws (28, 29) of which can be directed towards the tool extraction and spindle axes (Z), and a mirror-image jaw shape (30) to accept tools (WZ) with more than two different shank or taper sizes with at least three adjacent arc-shaped sections (a, b, d), the radii (ERa, ERb, ERd) of which match the different diameters of at least three shank or taper sizes, and in which the tool spindle unit (10) which is in the working position can be inserted into and removed from a holder and exchanged for a tool spindle unit (11) in a stand-by position. The at least three arc-shaped sections (a, b, d) of the jaws (28, 29) are at a distance (f) from the generatrix arcs with their centres of curvature (Ma, Mb, Md) on an arc aperture (KB) intersecting the insertion and removal axis (x), the generatrix centre (MKB) of which coincides with the centre of rotation (D) of the jaws (28, 29).