For rotational machines inducing new unbalance under service conditions, some different procedure from the usual balancing machines may be expected. For the above purpose, in this paper, an automatic liquid balancer, being improved from the previous reports, is proposed, the device consists of double cylindrical vessels. The inner vessel contains liquid available to compensate for rotor unbalance, and the outer vessel provides four sets of suction pipes and reservoirs. The results of experimental study are as follows. To control the liquid flow, a dam is necessary and, as for its shape, an oblique dam is the most effective. The device proposed is confirmed to be useful for balancing the rotor, and the whirling amplitude after balancing decreases to almost a constant value in spite of the location and size of the unbalance.