The tool-changing device has a changing head (7). By means of this, tool holders (4) with cylindrical parts (5) of different diameters can be inserted into a tool holder receiver (1). The changing head (7) has, at the end thereof which faces towards the tool holder (4) concerned at any moment, a substantially segmental part (7a) and a first centering recess provided in the latter, which first centering recess is formed by a part-cylindrical centering surface (8) having a radius corresponding approximately to the radius (R1) of the cylindrical part (5) of a first tool holder (4). Portions of a second part-cylindrical centering surface (9) are provided on the two opposite sides respectively of the segmental part (7a) on a part (7b) of the changing head (7) which is widened out in an axial direction with respect to the said segmental part, this second part-cylindrical centering surface (9) being concentric with the first centering surface (8) and its relatively long radius corresponding approximately to that of a cylindrical part of a second tool holder. The latter has near its radial screw-threaded bore a recess for the segmental part (7a). In the center of the first centering recess there is provided a connecting bolt which extends in the radial direction of movement of the changing head (7), is capable of being motor driven in either of two opposite directions of rotation at will and has an external screw-thread (10b) for engagement in the screw-threaded bore (6).