An NC-machine tool for working of large-size workpieces by turning, boring, milling, drilling, facing, and grinding is described. By inventive arrangement and installation of the individual machine units with respect to one another, by specially developed boring, milling, and facing heads, and by using special accessories for faceplate positioning, the above mentioned operations can be performed in one setting and without any additional transport mechanism. The machine tool can be used primarily for the manufacture of nuclear reactors.