PURPOSE: To avoid trouble on operation such as a roll slips, even in the case that the speed drops by the limitation on control of a motor controller by outputting a speed standard correction signal out of the motor controller, and inputting the correction signal into the motor controller to correct the speed.

CONSTITUTION: When current limitation is applied, a current limitation signal 31D becomes '1', and an 'or' circuit 45 outputs '1'. At this time, if the speed deviation gets over the value set with a setting means 42, the speed deviation large signal becomes '1', too, and the same signal as the speed deviation signal 41 is outputted as a speed standard correction signal 23A, and is used as the speed standard correction signal of other motor controller. Accordingly, the speed standard is operated to lower the speed of other motor controller by the amount of the speed of the motor controller having dropped by current limitation, so speed difference does not occur between motor controllers, and it becomes hard to cause roll slip.