PURPOSE: To improve response by a method wherein a first inverter control section performs supervisory control of a first motor and a first inverter and monitors an operation modifying request to be fed from a second inverter, and interlocking control of a plurality of motors are carried out directly through the inverter control section, without requiring the operation of a computor, upon occurrence of an abnormality.

CONSTITUTION: A computor 1 provides a command to a first inverter control section 2 for performing predetermined operation of a first motor 6. If a stop request of a first inverter 4 is not provided from a second inverter control section and no abnormality exists in the first inverter 4 and the first motor 6, at that time, the first motor 6 is operated through the first inverter 4. The first motor 6 is stopped upon provision of a stop command from the second inverter control section 3. Upon occurrence of an abnormality in the inverter 4 or the first motor 6, the first inverter 4 is stopped and a command for stopping a second inverter 5 is provided to the second inverter control section 3. In such a manner, first and second inverter control sections 2, 3 control the first and second motors 6, 7 alternately.