PURPOSE: To improve the efficiency of lathe operation by exchanging quickly the grip of a work having bean machined partially by the lathe of preceding process, and supplying it to lathe of next process without through handling.

CONSTITUTION: The work 2 having been partially machined is placed on a work carrying plate 3 by opening the grip exchanging hand H3 for a work, falling by specified amount, while operating the cylinder 7 for ascent and descent. Next, the grip exchanging hand H3 for work is elevated to the original position, while operating the cylinder 7 for ascent and descent. Then, the unmachined part W2 of the work 2 on the plate 3 is gripped by the first hand H1, while advancing the slide shaft again. Thereby, the machined part W2 and the unmachined part W2 in the work W2 having been partially machined, are mutually grip- exchanged.