PURPOSE: To prevent the occurrence of troubles due to vibration, by using a three-phase induction motor employing an inverter as a drive source to effect the starting and stopping of an intermittently driven automatic packaging machine which repeats the starting and stopping in conjunction with weighing equipment and feeder.

CONSTITUTION: An accurate and smooth starting and stopping are enabled by making use of a soft feature and torque constancy in the acceleration and deceleration time possessed by an inverter drive system. Said drive system has the unique feature of being able to change the number of rotations merely by adding starting and stopping signals thereto. Since the acceleration is effected for time t1 and the deceleration for time t2 and t3 at two stages, the starting and stopping can be controlled extremely softly.