The utility model relates to the field of machines, in particular to a device which is used for a common vertical lathe and can machine arc surfaces. The device comprises a tool fixture and an arc tool regulating mechanism, wherein the tool fixture is connected with a tool knife rest. The arc tool regulating mechanism comprises an arc regulating rod which drives a rotating tool regulating shaft, the tool regulating shaft drives an adjustable tool doing arc surface movement, and the tool regulating shaft is in rotary connection with a tool shaft fixture. One end of the tool regulating shaft is fixedly provided with the arc regulating rod, the other end is provided with the adjustable tool, and the tool shaft fixture is fixedly connected with the tool fixture. The device resolves the problem that a common vertical lathe can machine flat surfaces only and can not machine arc surfaces, and further resolves the technical problem of arc surface machining.