When a rotary table rotates, a main control section of a multi-tasking machine detects vibration of the rotary table on which a workpiece is mounted based on fluctuation of a position droop computed by a servo system. The main control section computes the arrangement position (the eccentricity amount and the eccentricity angle) of the workpiece with respect to the rotary table based on, for example, the detected vibration, the weight of the workpiece, and the rotation speed of the rotary table. The main control section computes the attachment position of a balancer with respect to the rotary table based on the computed arrangement position of the workpiece. Therefore, a suitable attachment position of a vibration suppressing balancer with respect to the rotary table is easily obtained.