NC (Numerical Control) lathes with two turrets are often used to achieve high efficiency of turning. To utilize them, it is very important to determine an optimal machining sequence by considering simultaneous machining, since combinations of processes influence practical cutting time very much. But it is difficult for users to determine an optimal machining sequence, because the number of combinations is great. A method is proposed to divide machining areas so that simultaneous machining may be the most efficient. The strategy is to check balances of cutting time for possible combinations of simultaneous machining and divide machining areas so that ill-balanced combinations may turn out well-balanced ones. After cutting directions of machining areas are determined, a balance table is generated. It classifies combinations into well-balanced ones and ill-balanced ones. Machining areas in ill-balanced combinations which require longer cutting time are divided so that cutting time of both areas will be nearly equal. Experimental results show that the method can generate NC programs with shorter cutting time than the conventional one does. The largest reduction in cutting time for the charts used on the experiments was 57 percent.